How to Keep a Pond Clean Without a Filter (Step-by-Step Guide)

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How to Keep a Pond Clean Without a Filter System (updated 2022 guide)

1) Make Use of Pond Plants

Benefits: Controls algae growth, adds more oxygen content, and helps remove excess nutrients from water.

how to keep a pond clean without a filter
Plants are great natural filters, making use of excess nutrients which can cause issues with water clarity.

Adding pond plants is one of the best long-term ways to keep pond water healthy and clear; and the more you can add, the better!

In-fact, for a wildlife pond without a filter, we’d say at least 60% of your pond should be populated by pond plants for maximum benefits. Plants provide a means of natural water filtration, absorbing excess nutrients, oxygenating water, and removing harmful substances. By absorbing nutrients and covering a large amount of surface water, plants will compete with nuisance algae and help prevent weeds from growing uncontrolled. The extra oxygen they provide improves the efficiency of beneficial bacteria so they can break down waste, and by removing excess nutrients water will be less cloudy overall. If you don’t have any plants in the pond you’ll have to carry out far more maintenance to maintain good water quality and clarity without a filter. As an added benefit, plants will also help attract wildlife, such as frogs, newts, and insects, which will help bring a natural pond to life in absence of fish.

For plant choices, we recommend a mix of submerged species, floating species, and marginal varieties. Only submerged plants will provide oxygenation to the water, but all will help reduce excess nutrients and remove harmful substances. For a full list of our favourite plants, check our main article on this here!

2) Provide Oxygenation & Aeration

Benefits: Adds oxygen, creates surface movement, improves beneficial bacteria, and deters mosquitoes.

air pumps for ponds without filters
Air pumps provide a direct line of oxygen to pond water, and are useful without a filter system in place.

Without a pump powering a filter system, you likely won’t have much aeration, and this can be hugely problematic for both wildlife and fish. Beneficial bacteria which are at the heart of a pond’s biological filtration system require large amounts of oxygen to function efficiently. In stagnant ponds with little flow aerobic (oxygen using) bacteria will die and anaerobic (carbon dioxide using) bacteria will begin to thrive. The problem with the second type of bacteria is that they’re slow-digesting, so will not be able to breakdown waste fast enough, and they also produce hydrogen sulphide as a by-product which will make your pond smell of rotten eggs.  As well as this, algae can quickly overtake a stagnant pond and mosquitoes love laying their eggs in slow moving water – both of which you should try to avoid to you want a clean pond.

Adding aeration in the form of a solar aerator, electric aerator, or even fountain display, will help improve oxygen content and surface movement. More oxygen will allow beneficial bacteria to thrive so they work more efficiently, and the added surface agitation will help prevent algae and mosquitoes from calling your pond their home. If you have goldfish in your filterless pond, adding aeration is even more important, as they’ll be competing with beneficial bacteria for dissolved oxygen on a daily basis. The more oxygen you can provide to your waters, the happier your fish will be in the environment.

3) Supplement with Beneficial Bacteria

Benefits: Boosts beneficial bacteria populations which improves bio-filtration and reduces waste.

beneficial bacteria in ponds
Beneficial bacteria treatments help boost natural populations and reduce waste.

Beneficial bacteria is responsible for the breakdown of harmful substances, such as ammonia and nitrites, into less harmful nitrates, which are used by plants as a fertilizer. This process is called the nitrogen cycle, and will occur in all ponds with enough oxygen, organic waste, and room for bacteria to populate. After a few weeks of having a new pond bacteria will begin to naturally colonize the pond, usually living on the pond liner and throughout the bottom muck that slowly builds. If you have a filter, they’d quickly populate the highly optimized filter media to easily breakdown substances that pass through so cleaner water goes back into the pond.

Even without a filter in the pond you can still boost the efficiency of your beneficial bacteria by providing plenty of oxygen, aeration, and keeping on top of waste levels. Bacteria will require a bit of waste to stay alive (it’s what they use for nutrients), so making a pond completely sterile is bad for biological filtration. The best method would be to add a form of aeration, such as a fountain or air pump, and then clean just the top layers of sludge every few months, leaving a small amount behind. In ponds without fish, a small amount of sludge is actually beneficial, as it provides bacteria with their energy resource, plants with their nutrients, and wildlife, such as newts, with a place to hide!

As well as aeration, topping up your ponds beneficial bacteria populations with a concentrated bacteria supplement will help keep levels high and reduce overall waste. We only recommend this 1-2 times a year, with the best times being early spring and early autumn where debris starts to build again.

4) Remove Excess Bottom Muck 

Benefits: Reduces excess nutrients, controls algae growth, and removes tannin (color) producing matter.

best pond vacuums
Water vacuums are the quickest way to clean bottom muck and sludge from the pond liner.

A little bit of sludge is healthy for a wildlife pond, as it provides nutrients for bacteria and plants, as well as a place to hide for frogs and newts. However, when a ponds waste levels exceed the pond’s biological filtration capacity, the eco-system will begin to suffer as oxygen content lowers and water quality degrades. If you have a small amount of fish in your filterless pond, you’ll need to clean out more sludge more regularly if you want to keep water quality good. Sludge won’t make water dirty by itself, and a small amount can actually promote cleaner water, but you should still keep on top of it at least every few months to ensure your pond is free of algae, has good levels of oxygen, and beneficial bacteria are not overwhelmed.

Since the largest majority of sludge is on the pond liner, the easiest way to clean it out is with a basic pond net or a more heavy duty water vacuum. If you have a small pond, a pond net can be used to slowly rake out the bottom muck whenever it gets too high. For larger ponds, or for better all-round cleaning, a pond vacuum can be used which will make short work of all kinds of debris. The problem with pond vacuums is they’ll also suck up small animals, such as tadpoles, newts, and frogs, so care should be taken during cleaning. For prevention, we recommend installing a high quality pond net which will help catch fallen leaves and twigs before they can sink in the pond and contribute to sludge.

As well as this, making sure your beneficial bacteria populations are healthy will help keep sludge in balance, and topping up with natural sludge eating bacteria can help boost your bacteria’s efficiency. The best time to clean a pond of sludge is the end of autumn in preparation for winter where ponds freeze over, as this is when fish are most vulnerable.

5) Perform Water Changes (If you have fish)

Benefits: Reduces excess nutrients, controls algae growth, and removes tannin (color) producing matter.

Activated carbon hose attachments can help remove chlorine from water during water changes.

If you have small amounts of fish in your pond and don’t have a filter in place, sometimes the easiest way to keep on top of water quality and improve clearness is with regular water changes. Water changes will usually be around 10-30% of water by volume, and can be performed by draining the top levels of water using a pump, vacuum, or siphon hose into the garden. Since pond water is packed with nutrients, we feel it’s a waste to simply put the water down the drain, so if you can you should use it for watering your garden plants as it acts as a great fertilizer!

Water changes will help reduce ammonia, nitrites, and excess nutrients if you water tests are coming back higher than safe parameters, and are also very effective at removing tannin (color) from the water. The problem with water changes is that they won’t solve the root-cause of water quality problems, but can work in a pinch while you sort out the underlying issues. For example, if you have a excess nutrients in the water making it cloudy, a water change may help temporarily, but the water will eventually return cloudy unless the source of the nutrients is reduced (i.e., excess sludge).

As well as this, water from our mains supply has high levels of both chlorine and chloramine – both of which are highly toxic to aquatic life. When performing water changes we always recommend de-chlorinating water before adding to the pond system, with the easiest methods being activated carbon hose attachments or de-chlorination treatments.

Keeping Ponds Clean Without Filters – Is it Possible?

how to filter water with plants in ponds
Keeping water clear without a filter can be difficult, but clean water can be achieved with plants, water changes, and good maintenance. Public domain.

The choice of whether or not to have a filter in your pond would depend on the number and type of fish you keep, the size of pond, and the overall biological load (waste levels) present. In general, the higher your bio-load, the more filtration you’ll need to maintain healthy water quality. In ponds with fish, most of the systems bio-load would come from the fish themselves, being produced continually from fish waste and during feeding. As waste levels are so much higher with fish, and due to the enclosed nature of a pond, it’s often very difficult to maintain a balance without the help of a filter box. The reason for this is because beneficial bacteria are at the heart of the filtration process, breaking down harmful substances into less harmful components – a process called the nitrogen cycle. Even though these bacteria populations comes naturally with ponds, the highest concentration will be within your filter box, which is why they’re so important for heavy bio-load systems.

On the other hand, in a pond with only small fish, or no fish at all, the bio-load will be relatively small, so healthy water can sometimes be maintained with good maintenance and natural biological filtration (bacteria). Plants, which act as natural water filters, regular water changes, bacteria supplements, and occasionally cleaning, can sometimes be all that’s needed to keep a pond clean without a filter in place.

Keeping Fish in a Pond without a Filter System (Do’s & Don’ts)

koi fish need proper water filtration
Small fish can often survive in a filter-less pond, but large fish, such as koi, would require a dedicated filter system. Public domain.

Before we expand on this topic, it should be stated that we always recommend having a dedicated filter system if you have fish in your pond. Even if your water quality is good, and your fish seem healthy, the problem with ponds is they can be subject to sudden changes in quality, which can negatively impact fish. The only time we’d suggest keeping fish in a pond without a filter is with lightly stocked goldfish in a heavily planted pond with regular maintenance.  Pond plants will ensure that excess nutrients and harmful substances are absorbed, whilst also working to keep away nuisance algae and weeds. Regular maintenance includes testing water quality, supplementing with beneficial bacteria, cleaning excess sludge, and performing small water changes when needed. If water tests are coming back good in your lightly stocked fish pond, with ammonia, nitrites, and pH being in safe parameters, then you’re maintaining a safe environment for fish keeping!

However, due to the enclosed nature of ponds, and how easily waste substances can build, it’s very difficult to maintain good water quality as stock levels increase. For ponds with lots of goldfish, or larger koi, a filter system is almost always needed to keep up with the biological load fish produce. Even though natural bacteria populations will help breakdown some waste, the most efficient breakdown will occur within the highly optimized filter box media which is designed to hold millions of denitrifying bacteria. Adding a filter will give you extra peace of mind and help safe guard your pond against dangerous fluctuations, making water quality more stable and healthy.

Maintaining Clear Pond Water Without a Filter Box

fallen leaves in pond
Fallen leaves are a common cause of water clarity problems as they produce organic color (tannin) when they decompose. Public domain.

Although filter boxes can help with water clarity, their primary goal is maintaining good water quality by reducing harmful substances. The most common causes of drops in clarity are excess debris, algae bloom, excess nutrients, tannin, or even sediment leaking into the pond. Many of these problems cannot be removed with regular filters even if you tried, but can be prevented with a solid cleaning routine and daily upkeep.

Water clarity can be improved by adding more pond plants, cleaning out excess sludge, installing pond netting, repairing leaks, and adding extra beneficial bacteria. Pond plants will compete with algae for nutrients and help prevent them growing, as well as provide natural water filtration by removing excess nutrients which can cloud water. Organic debris which falls into a pond will eventually decompose as sludge and leak color, called “tannin,” which will make your pond a yellow brown color but is overall not harmful. A bit of bottom sludge is good for a pond as it acts as a natural fertilizer, but too much can cause water clarity problems, so we recommend cleaning out a layer of sludge at least once a year to combat this. Since the majority of sludge in many ponds is due to fallen leaves and twigs, installing pond netting or a skimmer system is an easy way to prevent it from getting out of hand in the future.

A final thing you can do is make sure you have plenty of water flow and aeration, which can be from a waterfall, fountain, or pump system. Flow will stop insects from laying eggs in the water, which would contribute to waste, and will also provide more oxygen for beneficial bacteria to break down waste. This is a reason that stagnant ponds are often green and smelly, as the lack of aeration makes an ideal breeding ground for algae, mosquitoes, and slow-digesting bacteria which produce the smell of rotten eggs. In other words, fish or not, aeration is a good thing for all ponds!

Eco Filtration – Are Bog Filters (Plant Filters) Worth it?

natural bog filter for pond
Bog filters make use of natural pond plants to help remove harmful substances from pond water. Public domain.

If you don’t like the idea of a regular filter in your pond, but still want to improve water quality and clarity, you could consider opting for a bog filter instead. This is a more natural type of filter which works by slowly pumping water through a concentrated section of plants, which will work to absorb substances as the water passes through. Just like a filter box which has a higher amount of beneficial bacteria, a bog filter works the same as regular plants, although the higher concentration of plants and optimized water flow makes for better overall filtration.

Even though they’re very efficient in natural wildlife ponds, they’re not always the best choice for ponds with fish. A bog filter isn’t going to be able to provide enough filtration for heavy stocked ponds or koi ponds, so in these cases, you would still need to install a regular filtration system. For lightly stocked ponds with small fish, they’re an interesting alternative to normal filtration that can help with water quality and provide a more natural feel to the pond.

Sadly, if you’re not adding a regular filter due to technical limitations, such as no access to electricity, then even a bog filter may not be suitable. It may be more natural than a plastic filter box, but it still requires an electrical pump to move sufficient water through the main plant chamber for filtration to occur. For sites without access to electricity it’s often better to not include fish and instead opt for a wildlife pond, which will still look great by attracting frogs, newts, and a range of insects!

33 thoughts on “How to Keep a Pond Clean Without a Filter (Step-by-Step Guide)”

  1. Interesting opinions! I have a small wildlife pond which seems to be balanced ( except after the frogspawn has started to decay, when it temporarily becomes nutrient enriched). It has no filter but receives rainwater, diverted from a wooden barrel roof collecting system. The overflow goes downhill to a river at the bottom of the garden. Would the same system work with a raised pond of 600 gallons, in which I hope to keep a few orders, goldfish ( not Koi).

    • Hi Stephen,

      Thanks for your comment. Apologises for my slow reply.

      A natural pond without filtration is always possible, but only if you’re able to keep nitrogen compounds (ammonia, nitrites, & nitrates) within safe parameters for fish. Without filtration, regular water changes to remove excess waste substances are one of the best ways to achieve this goal. As you’ll have a natural rainwater and run-off system in place, and since you only intend to stock goldfish, I’d say this set-up would be pretty feasible if you can also keep up with general maintenance.

      However, my long-term concern here would be the potential for high pH swings in the absence of carbonates. Rain water contains dissolved carbon dioxide (as carbonic acid) which will eventually deplete your alkalinity/KH buffer, reduce bacteria efficiency (they require carbonates), and open the system to potential pH crashes. Calcium carbonate and magnesium carbonate make up the largest (and most important) buffer in fresh water eco-systems, but these are mostly found in hard (limestone) mains water or through manual supplementation. I’d say the system is good, but just be sure to keep a close eye on your water quality parameters over a 6-12 month period and note any potential problems with pH or water quality; and adjust accordingly.

      Good luck with the new pond!

  2. Hello. Great site! I dont have a lot of money but bought a second hand 160 x 160 fibreglass pond. It is 2 feet deep. I dont plan on keeping fish but would like to make it less deep. It also has a hole in it about 1 inch wide.. used previously for a hose/pump. I would like to fill it partly in with concrete covering the hole while doing so. Does concrete work for this? I am intending on using both a solar filtration kit and pond plants. I would be grateful for any assistance. Thankyou

    • Hi Steve,

      Thanks for the comment! Glad to hear you like the website.

      Yes, concrete should be fine for that job. My only advice would be to also consider a concrete sealer, such as “G4 Pond Sealer”, which will provide a protective outer layer to prevent potential leeching or deterioration. Just be sure to wait until the sealer is 100% dry before adding water, as most are toxic in liquid form to both plants and fish.

      Best of luck with the new pond! Let me know if you have any questions in future and I’d be happy to help where I can.

  3. This article was so helpful! Thank you!
    I plan to convert an unused hot tub into a pond/water garden, relying largely on aquatic plants to keep the ecosystem healthy. I thought to keep some minnows, too, to help prevent mosquitoes from becoming an issue. Do you have an idea of the number of minnows I would need? I don’t know the volume of the hot tub, but it looks like it seats eight people. The hot tub is also under a tree, if that informs your answer at all.
    Thanks again!

    • Hi B,

      Thanks for your comment. Very happy to hear the article was useful to you!

      Sounds like a very interesting project! Could I ask what type of minnows you’re looking at here? Stocking guidelines may differ slightly per individual species.

      Also, if you’re looking to combat mosquito larvae and pests, I would also recommend looking into mosquito fish. These are much smaller than most minnow species (especially species such as fathead minnows), so you can stock more per gallon of water, and they also love eating all kinds of insect larvae!

      You can find a more complete list with fish that actively eat larvae and their benefits/drawbacks for different kinds of ponds here –

      • This article is very helpful for a part of our Thesis. We are proposing a 31.5″ wide pond surrounding a monument. And I also saw your link about the Pond Fishes that eats larvae to prevent mosquitoes. Which of those fishes can be together in that particular pond? And what plants and species can also be part of that pond as a filter?
        Many Thanks! 🙂

  4. Your site is very interesting and informative. It has helped me understand the basic operation and necessities of our 200′ by 30′ pond. Ours has 4 skimmers, one of which feeds a bog, no filters and 4 aeration locations. Can you recommend a water testing kit suitable for this pond? We are located in Kelowna, BC, Canada. The pond just went in last year, but unfortunately our contractor has passed away so we are scrambling for information, maintenance, etc.

    thank you in advance for your input!

  5. Hi pond informer Taneesha here i want to know how to keep the pond clean without usng a filter because we are building a natural resorse pond with fishes


  6. Hi love your site very interesting,
    Just wondering if you can advise me please….
    My pond I’d about 6ft x 5ft and have a lot of fish (they keep spawning and producing more babies) and not sure what I can do about that,
    But my pond has started to lose water so I have turned off the pump to investigate and I was wondering how long would it be safe without the pump and filtration system on., just to add to the problem I’m going away for 3 days, any advice would be very helpful. Many thanks in anticipation.Diane.

    • Hi Diane,

      Massive apologies for such a late reply! Thank you so much for visiting the site, and for the compliment! It’s wonderful to hear feedback from readers 🙂

      What species of fish are spawning? Each species has different requirements for spawning, so knowing that can help us to determine how to go about lessening or preventing further breeding. In terms of your pump and filtration system, I wouldn’t leave it like that for more than a day or two as dissolved oxygen levels can deplete very quickly, particularly with your fish spawning and many babies being present.

  7. Hi such a helpful site, thank you. I have a wildlife pond about 18 x 8 metres, depth average about 0.5 metres, probably 45-50,000 litres. Fish are rudd and tench plus one larger common carp about 4lbs weight. Lots of marginal plants, and water lillies covering about 30% surface which are mainly free-rooted. I net it from autumn to spring but the plants/fish create plenty of sediment, water used to be very unclear.
    Have just installed a big koi type filter…it works superbly, water much clearer, BUT cleaning the filter is needed every couple of weeks as it catches so much gunk. I don’t fancy doing that throughout the winter but am told the filter should run 24/7/365. I have various questions, all to see if I can cut down on the gunk & need for so much filter-cleaning.
    1.Would potting all the lillies cut down on gunk a lot?
    2.Would getting rid of the big carp do the same (he roots around a lot)?
    3.Would adding more bottom-feeding fish eg tench, gudgeon, help?
    4. Could I switch the filter off between October & April if I add in bacteria when I re-start it?
    If I do do that should I add an aereator to run during the winter months when filter is off?
    5.I have been cleaning the filter completely until water runs clear through it (tap water) – should I not clean it so thoroughly but leave some gunk in it?
    6. Given that I’ve cleaned it thoroughly with tap water for a couple of months now should I introduce some bacteria (into pond or into filter)?
    7. Would adding more floating plants help the health, ‘tho would need a lot given the area?
    Thank you very much!

    • Hi Mike,

      Sorry for the slow reply! My work has been keeping me very busy these past few weeks. I’m very glad to hear the site has been helpful to you!

      To answer your questions:

      1) This may actually increase gunk over time, as the lilies roots will be removing a large quantity of excess nutrients/waste particles, but whether potted or not, they’ll still drop foliage into the water contributing to overall gunk.

      2) Although this wouldn’t remove the gunk itself, it would probably prevent some muck being kicked up and making it’s way into your filter system. However, your pond is quite large, and a single carp is unlikely to be the main cause here. All fish, as well as the insects, wildlife and even the weather, are likely contributing equally to muck being lifted.

      3) This would almost definitely result in more muck/gunk being lifted from the pond floor and the filters clogging even faster! Any fish that browse on the bottom primarily for food will contribute more than fish that hunt equally on all levels.

      4) How are your water quality parameters? ‘Dirty’ water doesn’t always mean unhealthy water, and many wildlife ponds I’ve worked on have been very mucky but still have had good general water quality. If your water quality was good before adding the filter, and the filter is mostly just improving clarity now, I think turning it off for winter is perfectly fine.

      5) Could I ask what type of filter (brand/model/capacity) you have? In general, having too much gunk on filter media is actually detrimental, as bacteria that break down waste compounds require plenty of oxygen to work efficiently, otherwise they’ll quickly die off. A thin layer of slime is fine, but in my opinion, it’s often better to clean a little too much than too little, as bacteria will re-colonise clean media extremely quickly in a established pond, but will struggle if the surface is covered in gunk.

      6) If your water quality test results are showing normal/low ammonia and other waste compounds, there is likely no need! Your pond sounds very established and healthy, so you’ll have a huge abundance of natural bacteria present and ready to take over the filter media again.

      7) Any kind of plants will help remove excess nutrients (and to an extent, the actual sludge), but they will also drop foliage, seeds, and pollen which will contribute to the bottom muck. If your water quality test results are showing low ammonia and healthy parameters, more plants likely would not help much and would be more a personal choice.

      If I was in your situation, and building on the above advice, I’d firstly take a broad range water quality test and take note of readings for ammonia, nitrites, nitrates, pH and KH (alkalinity). If waste compound parameters are looking good, this indicates to me that the water is healthy and bio-filtration doesn’t need extra help (bacteria supplements, more plants etc.). It also indicates that the levels of muck/gunk are not so high that they’re causing major issues, so the decision on whether to lower them would be another of personal preference. If the muck is constantly causing the filters to clog due to being stirred up, and you wanted to reduce this, simply vacuuming around the shallow banks and areas closest to the filter pump/in-take may be a good way to reduce filter cleaning. Most electric vacuums will reach much deeper than 0.5m, and I personally think they’re almost essential for larger water bodies, especially to keep on top of muck. Obviously plants, wildlife and fish all require some muck to survive, but simply cleaning a small area around the filter and pump may be all that’s needed to prevent major clogging.

      Alternatively, you could try installing a regular skimmer system to catch floating debris before it sinks, or check into a floating lake skimmer system designed for water bodies with changing annual water levels.

      More articles on these topics below if you’d like to read further:

      Hope that helped! Let me know if you have any other questions.

  8. Hi Chris – that is fantastically helpful, Thank You!

    Water quality – I’ve assumed it’s fine as the pond is very well established (a few rudd die every year but they breed there so some may die of old age); I have just ordered the NT Labs Multiple kit and will post the results over this coming weekend and will be hugely grateful for your reaction and view on whether I can turn the filter Off October-April, and if & when I need to add bacteria.

    The filter type: it is made by Kockney Koi who describe it as – The KF18,000V is a high quality, free-standing, fibreglass, four bay, filter with integral vortex designed to improve your fish’s environment. The unit is suitable for fish ponds of 18,000 litres and a maximum flow rate of 11,000 litres per hour. However, with lighter stocking densities or in fish free ponds the KF18,000 will comfortably cope with much larger volumes.
    The media package consists of:
    Bay 1: Eighteen 16″ long x 8″ diametre polypropylene filter brushes – They are of a semi-rigid construction with a wire loop at the end for easy cleaning.
    Bay 2: Blue matting – This is an excellent filter media as it has a large surface area giving it an excellent bio-mass retention. Its open texture removes larger particles from the water.
    Bay 3: Three layers of reticulated foam with different density of porosity of each layer. This is on top of a layer of approximately 2 cubic foot of flocor.
    Bay 4: Six way foam block manifold assembly on top of six cubic foot of Flocor. The large surface area of Flocor tubes makes it an ideal filter media.

    Back to me: re pond vacuums – do you know if Matala are available in the UK (nothing shows up on google)? And do you know of/have views on the ‘PondHero Sludge Muncher 1400W’ one?

    Huge Thank You again, I will be back to you with the water test results.

    • Hi Mike,

      That filter is a great model! Good choice, and ideal for your size of pond.

      Your water quality test results look good to me. Could I ask, was the pond around a long time before you added the filter system? If so, were the fish happy and healthy? No problems?

      If so, my guess is that your pond already has a huge quantity of biological filtration (natural bacteria) present throughout the whole system due to its size and maturity. You’ll have bacteria on rocks, plants, edges and all over the surface of the bottom. Even without a filter for a few months, I think your water quality would likely hold strong, and you may not even see a drop in water clarity until Spring when temperatures begin to rise and wildlife and fish become more active.

      Water quality is less of a concern in winter as fish produce less waste, they browse much less, and decomposition of organic material slows. The main reason why you may have been recommended to leave your filter on in winter isn’t so much for waste compounds, but for aeration and oxygen. During winter fish and animals still require dissolved oxygen, and if the top of the pond freezes, oxygen cannot dissolve into the system and carbon dioxide cannot escape. Running a pump/filter is often the easiest way to counter this, but you can also do it in other ways, such as with de-icers and aerators. De-icers just float around the surface and create air holes in the ice, allowing gas exchange to take place even if the rest of the pond is frozen. Powerful aerators are even better, as they will keep the top ice free and directly oxygenate the water. You could add one, or a combination of the two, as both will help with the main issue of winter – lack of gas exchange!

      In terms of the filter, I’d advise you empty it out until spring. The water inside will quickly become stagnant and low in oxygen, which will result in all good bacteria (aerobic – oxygen using) dying off anyway, and come spring, it’ll start smelling due to an increase in bacteria that thrive in poor conditions (anaerobic – carbon dioxide using). Drain it, clean it, and cover it for the season. Come spring, simply start it up fresh and let the natural bacteria in your pond re-colonize the clean media. You could add supplements to speed this up, but I don’t think it’s necessary in such a mature pond, but adding more never hurts either!

      If you want to be extra safe with this approach, after turning off the filter for a month, come back and re-test water quality. If results are still good, I don’t think you’ll have any issues for the rest of the season and can simply wait until spring to turn it back on. If they’re only slightly worse, perform another test in a week or two to see if they’re holding. Also I’d be happy to help if you would like to report results at a later date!

      Finally, in terms of the pond vacuums, I don’t think Matala trade in the UK, and I wasn’t able to find any distributors outside of the US. I’ve never used the PondHero vacs, but the reviews look ok. Just be sure to check the specification sheet to ensure the pole length and suction depth is adequate for your size of pond! Although Oase vacuums are expensive, I’ve operated them for years and years with heavy use, and can vouch for their reliability. I can’t say how reliable the PondHero is, but Oase vacuums are always a safe best in my book.

      I hope that helps. Let me know if you have any more questions, and sorry again for the delay. I try to keep on top of comments a few times a week, but it’s been a busy end of season for me, so I’ve been a little slow on the website side of things!

      Including a few links below for further reading and to answer some of your other questions:

  9. Have done the tests with the NTLabs kit (another Thank You – a really neat product!) and every test is ‘Good’ – it did take a lot of drops to get the colour change on KH Alkanity (7 to 8 drops) and on GH Hardness (12 drops) but that is probably just because we are in a hard water and chalky area – i hope that’s the reason?!

    So – do you think I’m OK to turn filter Off October-April? Details of filter in earlier post, above.
    If so do I leave it empty, or with water in it – if so ‘fresh’ water from pond just after cleaning it, or water that’s been running through for a while that’ll leave some gunk in the filter?
    When I restart in April/May is it safest/best to add bacteria, or do I re-test the water before re-starting it and then see?
    And if best/safest to add bacteria at re-start any suggestion as to which type I buy?

    Would love to know any answers to the 2 questions in earlier post about pond vacs too.

    Thanks so much for SUCH a helpful site and service – really invaluable. THANK YOU!

  10. Another huge Thank You for such a clear & comprehensive answer – I cannot tell you how helpful and appreciated your input is.

    Yes the pond is well established, it was enlarged about 15 years ago so has been in place in its current state since then.
    The fish have been in good health apart from about 2 to 3 years ago when rudd started dying: I then had it drained and we scooped out a lot of sludge and started again, and then 3 months ago had a big clean up removing much sludge and lots of hornwort (without draining it fully) and put in the filter, since when the water clarity has improved from completely murky to very clear.

    Historically both rudd & tench have bred in it – I worry now that it is so clean and clear will this hinder the fish breeding (they must feel very exposed now!)?

    I was also thinking of, next spring, adding some more tench and adding some gudgeon but given that it is a much cleaner less muddy environment now is that a good idea?

    Thank you for the links – the ones to aerators are for USA models – are there recommended UK aerators that will work for my size of pond (45-50,000 litres)?
    ‘Tho I guess that if a ‘smaller’ aerator is working in the deeper part of the pond where the fish will congregate anyway in the winter that that will suffice.

    Thank you again for invaluable help.

    • Hi Mike,

      I’m actually not too sure how much water clarity will affect the breeding of those fish, but it would be interesting if you do happen to note any changes in their behaviour. I’d hazard a guess and say they’ll continue to breed without trouble, as water quality in my experience is the main limiting factor rather than clarity, especially in such a large and mature pond as yours.

      If water quality is good, I don’t think adding more fish will be a problem so long as you remember to test regularly to ensure the pond isn’t becoming overstocked. Adding fish in smaller numbers, waiting a month or so, testing water quality and observing clarity, and then possibly adding more, might be the best way here to ensure a good balance is kept.

      Ah, sorry again! I actually thought some of these might have been available in the UK (I could have sworn I saw them somewhere!), but it seems I’m mistaken. Yeah, it’s much easier to find larger commercial air compressors in the USA as ponds are, in-general, larger than their UK-counterparts.

      In terms of off-the-shelf aerators, this Blagdon model was one of the best I could find (up to 11,000 liters with fish – which isn’t bad!) –

      An aerator does not need to stretch the whole system, as the dissolved oxygen will spread naturally and a smaller one should still be strong enough (assuming pond depth matches aerator spec!) to keep ice away in winter and allow gas exchange to take place.

      For larger models, you’d need to contact specialist retailers as they’re not so readily accessible in the UK. Examples below:

      These are likely to be much more expensive, so it may be better to simply pick up one or two of the cheaper models and place them strategically throughout the system. Fish will instinctively be attracted to areas of higher oxygen and better water quality anyway, so they’d likely congregate around the smaller aerators if they ever needed to.

      Do keep me updated on the pond situation if anything happens in future! It’s always very interesting to hear from someone with a much larger pond and less common fish species.

      Let me know if you have any other questions!


  11. Thanks again Chris – you are a Star!
    I will certainly keep you updated and come back with any further Qs.
    Next steps – get into pond to cut back & remove all the dying leaves & foliage, then stop the filter & clean it out, whilst putting in the new aerator for the winter.
    All thanks to you.

  12. This is excellent information, thank you! I acquired a pond (approx. 6 ft. long and 3ft deep) from a friend who no longer wanted the upkeep and installed it on my heavily wooded property in late spring (in a mostly shaded area). I don’t have electrical capability where the pond is located. About 80% of it is filled with plants (hyacinth, water lettuce, etc.), and inside are 5 adult goldfish and a myriad of frogs, newts and an occasional turtle. It is rain-fed only (no filter nor spring).The goldfish reproduced this summer and there are a few little ones in the mix now. I’ve never checked the water quality but it looks quite clear, it doesn’t smell at all, and the fish are fat and seem happy. I plan to keep the ice at bay this winter to keep oxygen levels up, and I’ve been skimming the leaves off the surface this fall (I live in Pennsylvania). Should I remove the surface plants once they begin to die after the frost? Is there anything else I should add to keep the fish alive during the winter? I can’t install an electric filter. Thanks for any input!

    • Hi Bethany,

      Sorry for the late reply!

      It sounds like you have a wonderful natural ecosystem going! It can be quite difficult to maintain a healthy pond without any aid from filters or pumps, so kudos to you! Particularly in Pennsylvania with so much vegetation about (it’s a gorgeous state, but certainly lots of leaves!). I would suggest that you do perform daily water quality checks, just to be sure. Seemingly small things like air temperature shifts, more leaves than usual falling into the pond, etc. can really alter water quality more quickly than one might think.

      In terms of the plants, yes any dead/dying plants should be removed from the water to decrease decomposition and oxygen demand in the pond. If the plants are perennial, you can simply trim them down to a few inches below the water’s surface, this way they can overwinter more easily and should be able to simply resprout the following spring. Annual plants can be moved indoors for the winter if you wish to keep them for the following year, or they can just be removed either before or after they die off.

      For overwintering your fish, you should try to find a way to keep the water mixed up during the winter, so that it doesn’t freeze. I know you mentioned that you don’t have electrical capabilities where the pond is located, but there are some battery operated pumps as well as heaters available that will help to keep the water continually mixed and at a livable temperature. In addition, whether or not your fish can survive outdoors for the winter depends on their species. Please get back to us with that info and we can help you both with your concern about breeding and overwintering.

      Thanks for reading and commenting!

  13. Hi
    I dont know if anyone else does this but we have an outside pond no pump no filter but we have goldfish in there and we don’t feed them but they have always lived. We have plants in there and do pick out the leaves. It gets cleaned out like once a year. We have some algae at the moment should I just skim it out with a net? Also we have 1 goldfish with fungal infection what is the best stuff to get? And should I treat the whole pond with it?

    • Hi Grace,

      Thanks for reading and commenting! Could you describe the algae to me? Some types of algae are actually beneficial to ponds, so long as there’s not too much of it. How much of your pond has algae would you say, and has it always been there? If just a small portion of your pond has algae and it’s been there for quite some time without harming your fish, it’s likely safe to simply leave it. However, you can skim it out with a net like you mentioned as well! Alternatively, here are some other methods as well:

      The presence of a fungal infection tells me that you likely need to monitor your water quality more closely, and I would urge you to perform weekly water changes of 15-25% to maintain healthy water quality, particularly since the pond gets cleaned once per year. To treat the goldfish, you can quarantine the one for treatment that has visible symptoms, and treat with a salt bath, potassium permanganate, acriflavine, and several other products as gone over in detail in this article: Though the article mentions koi, many of these fungal ailments affect goldfish as well, and the treatment options will work just the same. Be sure to closely follow the instructions on the product label, no matter what you decide to get! I would urge you to treat your entire pond rather than just quarantining the one fish, as fungal infections can take some time to show up and it may be present in the rest of the pond without showing visible signs yet.

      I hope that this helps!

  14. Hi, thanks for getting back to me.
    The goldfish has now sadly died.
    I have about 4 or 5 goldfish in the pond and they seem fine at the moment. The algae is a recent thing really and is taking up about a quarter of the pond. The water is very clear but its probably not the best quality we never do water tests and the water doesnt really ever get changed. I’d have to change the water with a bucket as thats all I have how many buckets would equate to a 25%
    water change the pond is about 100 litres. Also we’ve only ever filled it back up with rain water from our water butts is this ok? Once this is done shall i still treat the water for the fungal problem?
    Thanks so much for your help

  15. My well produces 10 gal a minute 24/ 7 I wanna use that water flow and make a pond 10′ by 22 with no Filtration In a small amount of fish would you recommend that

  16. Hi there
    We have a large pond about 10mx10mx1.5m.
    It was here when we moved in but the air pump does not work.
    Do we need to replace it or will the pond take care of itself.
    The existing pump is a Hailea

  17. Hi, the water in my pond has turned brown. It seems to be fine soil particles but the result is that it is impossible to look down into the pond. Can you advise me on the best method to clear the water? The pond still supports life. The frogs have recently spawned but, as I have said, the water is muddy and it doesn’t look good.

    • Hi Dermot,

      Do you have many plants, either submerged or marginal? Turbidity can be a result of a number of things, including a potential water imbalance or a lack of plant matter to help hold the soil in place. Turbid water, as you’ve noticed, isn’t necessarily a detriment to the pond’s inhabitants, but there are some steps you can take to clear the water so you can see and enjoy your pond. You can incorporate an aerator and filter to help oxygenate, circulate, and clean the water; the aforementioned submerged and marginal plants can be helpful; some chemical treatments, like gypsum, can help to essentially weigh down the particles if the issue is due to a mineral imbalance; checking for and removing any built-up sludge on the bottom of the pond; adding in beneficial bacteria to help break down organic waste; and performing a heavy water change or two (though this could certainly impact frogs and other wildlife).

      We have an in-depth article on causes and solutions for turbid water here if you’d like to read more about this:,can%20usually%20be%20attributed%20to%20a%20single%20cause.

  18. Hi

    Thanks so much for these tips. I have a natural spring in the garden which our predecessors dammed to make a pond about 2x3m. It’s maybe 60cms deep, plus a bottom layer of mud about another 20 cms. It’s covered with lily-like plants, but I have cleared out about 1 m2. The water is very cold (from a ground spring) and very clear. It has a glow rate of maybe 5-10 litres a second.

    There is no filter or pump of any kind, and I don’t particularly want to install one.

    I was hopping I would be able to stock the pond with, maybe, a dozen smallish goldfish. I don’t think I can be relied upon to remember to feed them regularly!

    Is this a runner? Or should I leave it to the frogs and newts etc?

    many thanks



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