How to Keep a Pond Clean Without a Filter System (updated 2019 guide)
Benefits: Controls algae growth, adds more oxygen content, and helps remove excess nutrients from water.
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 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, 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!
Benefits: Adds oxygen, creates surface movement, improves beneficial bacteria, and deters mosquitoes.
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 ponds 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 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 they’ll be in the environment.
Benefits: Boosts beneficial bacteria populations which improves bio-filtration and reduces 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 it’s energy resource, plants their nutrients, and wildlife, such as newts, 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.
Benefits: Reduces excess nutrients, controls algae growth, and removes tannin (color) producing matter.
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 ponds 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.
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?
The choice of whether or not to have a filter in your pond would depend on the 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)
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
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. 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 is getting out of hand in 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 laying eggs in the water, which will 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?
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!