How to Clear Cloudy Pond Water (And Keep It Clear)

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How to Clear Cloudy & Murky Water in Garden Ponds 2022 (Top Methods)

Many koi fish in a cloudy pond
Cloudy water can make it difficult to see fish, and could be a symptom of a growing water imbalance. Public domain.

Cloudy water can be a bit of a nuisance for us pond owners, making it more difficult to see fish and giving the water an unpleasant “muddy” appearance. Most of the time a clouded pond is only a temporary issue, but it can also be accompanied by other problems, such as algae growth, or be a symptom of a growing chemical imbalance. New ponds tend to have issues with water becoming slightly murky while they become established, but cloudiness can also affect mature ponds, too.  Common causes of cloudy water include bacteria blooms, excess nutrients, algae growth, tannins, debris buildup, or even changes in the weather!

If you notice your water has become cloudy suddenly and you have fish, it may be a good idea to test the water to make sure there are no problems with water quality. A pond without fish may look unpleasant with cloudy water, but since there are no living organisms, it is often safe to let the pond try to balance itself out naturally instead of immediately treating it. If you have goldfish or koi, the issue should be checked more thoroughly to ensure your fish are not at risk from a growing problem or substance imbalance.

Luckily, cloudy or milky pond water is not something that usually causes major problems, and 9 out of 10 times it will resolve on its own naturally as your pond balances itself out. Even so, it’s still good practice to test pond water when you notice changes in clarity, and there are also things you can do to help fix the cloudiness if it just doesn’t want to go away.

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Why is my Pond Water Cloudy? (Top Causes)

1) Newer Ponds

Newer ponds, especially those not cycled correctly, may have several weeks (or months) of cloudy water while the ecosystem becomes established. This is actually the most common time we see cloudy water, and generally, it resolves naturally as the pond matures and finds a balance. The cause is likely due to a combination of bacteria growth and waste buildup after your new fish begin eating regularly. If a pond is cycled correctly before adding fish there should be sufficient bacteria present for waste breakdown, but if fish are introduced to a pond without bacteria, you can have all sorts of problems with water quality, with a symptom being cloudy water.

2) Beneficial Bacteria Growth

A rapid bloom in bacteria growth can contribute to cloudy or murky pond water, and can affect both new and mature ponds. Although more common in fresh ponds being cycled, a bacteria bloom can also occur in a mature pond under the correct conditions. For example, if you have an older pond and have performed a heavy water change and supplemented with beneficial bacteria, your water may become cloudy for a few days as the new bacteria settles in. New ponds have no bacteria to begin with, so when cycling a pond new bacteria tend to grow rapidly, and this growth causes the water to become murky.

3) Excess Nutrients, Waste, or Debris

Beneficial bacteria are needed to break down organic matter, such as sludge and fish waste, or it simply builds in your pond to dangerous levels. A lack of beneficial bacteria or lack of water filtration may be a cause of excess nutrients or harmful substances in the water. Excess nutrients may also be caused by overfeeding fish, leaves falling in the pond, or sediment leaking from plants or the surrounding soil. It may also be caused by a leak in the pond liner, in which nutrients are seeping into the water slowly over time.

Debris can also cause issues with clarity, with free-swimming finer particles sometimes being too small for filter media to remove. As these small particles build up in the pond, the water becomes more and more murky in color and appearance.

4) Nuisance Algae Growth

cloudy pond with algae
If water is cloudy and tinted green, it’s likely the result of algae overgrowth. Public domain.

Murky water that also looks a little green is likely caused by nuisance algae growth. As algae grow they leak tannins (organic color) into the water, causing it to become green and cloudy in appearance. They also contribute to sludge buildup as they die off, and this reduces oxygen levels as bacteria work double-time to break down the new waste. Algae can also affect the pH of water by removing dissolved carbon dioxide during photosynthesis, which causes a drop in acidity over time.

5) Problems with Water Quality

A general problem with water quality may contribute to murky water, which includes swings in pH or a spike in ammonia levels. The best way to determine if the issue is related to an imbalance is to test your pond water, particularly looking at readings for pH, ammonia, nitrite, and KH. A very high (or low) reading on certain measurements could be related to a problem elsewhere in the pond which is causing problems with water clearness.

Steps to Fix Cloudy or Murky Pond Water

Step 1: Test Water Quality

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The first thing to do when you notice your water is becoming cloudy is to test it for potential problems. This applies both to new and mature ponds, as both can have issues with water quality. For newer ponds that aren’t correctly cycled before adding fish, the problems are usually from high ammonia or a swing in pH. The lack of beneficial bacteria in an uncycled fish pond means there is no effective means of removing waste, particularly if other natural decomposers are lacking as well, so ammonia begins to rise. For mature ponds, it could be a combination of different things, and it would be impossible to pinpoint the cause without further testing.

The best way to determine if you have a problem with water quality that could be causing the murky water is with a water test kit. These provide an “all-in-one” method of testing the most important measurements, such as ammonia, pH, nitrites, and sometimes KH. Ammonia is a standard measurement for most tests, and the ideal value is as close to zero as possible. Ponds don’t need ammonia, so the less there is the better for water clarity and fish health.

Water pH should be within 6.5-8.5, but a more ideal value for fish would be 6.8-7.8. A rise or fall in pH is often caused by a low KH measurement, which is a measure of dissolved bicarbonate and carbonate ions in pond water. These act as buffers in your pond water, preventing rapid changes in pH and maintaining a more stable environment.

For more information on testing water quality, check our full guide on this here which includes the best test kits and information about ideal water values.

Step 2: Optimize Filtration

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Murky or cloudy water could be caused by waste buildup or free-swimming particles not being removed by your filter. Biological filtration has the task of breaking down organic matter and converting harmful ammonia into nitrites, and then into nitrates which are used by plants. This process is carried out by millions of beneficial bacteria living on your pond floor and inside your biological filter media. If you have a build-up of waste and ammonia (which a test kit can determine), your biological filtration may need improvement. This could be as simple as adding more beneficial bacteria to the filter box, or may require a better filter system or more optimized bio-media. Making sure your filter box is the correct size for your pond and bio-load (fish waste) is important, and often ponds which are heavy fish stocked may benefit from a larger filter. If your filter box is the correct size, adding beneficial bacteria to the pond or trying a new type of bio media may be the best option.

As well as this, very fine particles of debris may be causing the murky water and your regular mechanical media may be too course to remove them. Adding a very fine media to your filter, such as poly-wool, is a great way to remove very fine debris and tannin (color) from pond water. If you have a pressurized filter, it is better to add the poly-wool in front of the filter output in a basket, as the media can cause a huge buildup in pressure. The media would need to be replaced once it becomes clogged until the desired clarity is obtained, and this may take a few weeks depending on the amount of debris.

Step 3: Reduce Sludge and Excess Nutrients

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Fallen leaves in a pond
Sludge is often caused by a buildup of debris, like leaves. Public domain.

Excess sludge and nutrients in a pond can contribute to murky water, lower oxygen content, and cause spikes in ammonia. If you have a buildup of sludge along the pond floor it may be best to remove it, especially if you have fish. A small amount of sludge is natural and actually beneficial to plants, as it acts as a natural fertiliser. Problems occur when waste builds up to high levels which bacteria cannot effectively control, so it should be cleaned out manually. Sludge can be removed easily with a pond vacuum, or can be broken down with natural sludge remover products. If using sludge removers you will need to regularly clean your filter media, as this is where most debris will end up! If you have very heavy sludge, often a combination of vacuum and sludge remover is best. This works particularly well when preparing your fish pond for winter to ensure the maximum amount of sludge is removed.

Sludge is caused by organic debris that falls into your pond and sinks to the bottom, with the highest contributor usually being fallen leaves (especially in autumn). The best way to prevent sludge from building up too high is to stop the debris from entering your water in the first place! This can be achieved with pond netting to catch leaves, or pond skimmers to remove floating debris before it sinks.

Issues with water clarity may also be related to overfeeding fish (excess nutrients), or by using low quality fish feed which is contributing to excess sludge. Reducing the amount you feed fish and monitoring their eating habits can help you work out the correct quantity. Food should also be gradually reduced as the weather gets colder so you can prepare your pond for winter.

Step 4: Control Algae Growth

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If your pond water is cloudy and also slightly green in color you’re likely dealing with a bloom of green free-swimming algae. If left uncontrolled, green algae will eventually turn a pond into a thick green soup, and cause all sorts of issues for fish. Larger forms of algae, such as string algae, are unlikely to directly affect water clarity, but these can still be an unpleasant feature for a garden pond. You can read our full guide to different types of algae here, and their possible effects on ponds.

Luckily, green water algae can be removed easily with a UV clarifier and plenty of filter media maintenance! A clarifier is our recommended choice for reducing green algae as it’s safe for fish (unlike algaecides) and also helps reduce harmful free-swimming bacteria. If your water is just becoming murky and green in color, you likely won’t need to run the clarifier for long before you see the difference. If the bloom is particularly heavy, you may need a few weeks of constant operation until water becomes clear again.

However much algae you have, make sure to regularly clean your mechanical filter media! As the UV light destroys the algae it will become trapped inside your filter box and quickly clog the media. Daily cleaning may be required until you see a good reduction in green water, or you risk greatly reducing your pond’s overall filtration. Beneficial bacteria can be supplemented to help with the breakdown of dead algae, and extra aeration (i.e., air pump) installed for increased oxygen as the bacteria work.

Step 5: Give it time!

For most ponds, especially new ponds or fish-less ponds, cloudy water will resolve naturally as the pond ecosystem becomes established. Even in a fish pond, if your tests come back all clear and you don’t have issues with sludge or algae, your pond may just be going through a natural cycle. For example, changes in temperature between seasons or sudden heavy rainfall can have an effect on pond water and cause temporary murkiness. Unless there is a problem you can pinpoint, such as high ammonia or green algae, your pond is likely fine and just needs time to re-adjust.

This is especially true for new ponds, as a new pond has no mature eco-system in place and it needs to find its “feet” before it can walk comfortably. This may take a few months, or even years, and it will likely change appearance during the process. Eventually, however, once a pond has matured, you will rarely have issues with clarity so long as you keep on top of maintenance.

Unless your fish have changed in their behaviour or are showing signs of sickness, cloudy water is likely nothing to worry about, but you can still test your water for extra peace of mind!

24 thoughts on “How to Clear Cloudy Pond Water (And Keep It Clear)”

  1. My fish pond has suddenly become cloudy with fine black particles. Is it likely to be result of sustained hot sunny weather

  2. Hi. My pond water is looking a bit cloudy since yesterday, i have done a water test and all was ok except the KH so i put in the right amount of KH powder and also some salt ready for the winter, i have got 2 12000 Laguna Pressurised filters running, and 1 Eazy Pod filter running also, i have 2 Skimmers collecting the leaves, and i also scoop any leaves out there may be every day when i go out to look and check on my fish, is it due to what i added yesterday or am i doing anything wrong, any info is appreciated thank you.

  3. Hi

    My pond became very cloudy since end of November this year.
    I had it cleaned before the winter, good clean of the filter (where I did used the pond water, and running fine and crystal clear, in early November), the cloudy pond appeared a week after I stopped feeding my koi’s because the temperature drop to below 10c in late November, I checked the filter looks clean, I thought the pump was blocked tried to remove the debris, but it doesn’t help.

    My husband turned the opening of the suctions to less than a quarter because the fish got sucked when they swim too close to the pump, but the turned down suction opening didn’t seemed have any problem until I stopped feeding the koi’s in late November.

    What do you think I am worried about my koi’s. No algae. Just murky, cannot see my koi’s anymore.


    • Hi Hong,

      Thanks for your comment and question!

      Have you performed any water quality tests recently? If water quality tests are coming back ok (e.g., low nitrogen compounds and stable pH/KH), I’d say this is just due to the natural fluctuations in water temperature. In-fact, I’d say cloudy water is the most common at the end of autumn and start of spring, as temperature begins to both fall and rise quite rapidly during these periods. If there is some leaf build-up on the pond floor from autumn, you may also have some excess tannin contributing to the murkiness.

      In any case, so long as your water quality is within safe parameters when testing, I don’t think the cloudy water is anything to worry about and should clear naturally over the winter period as temps begin to stabilize.

      If you’d like to quickly clear some of the murkiness to better view your koi, adding activated carbon to the filter or a fine mesh media to the filter out-take to collect the tiny dissolved tannin/debris are both effective solutions for obtaining clearer water at all times of the year.

  4. We have a new algae this year…it looks like white clouds clinging to the rocks bordering the pond …we have a rubber bottom large pond with no filtration fish…do you know what this algae type is called or how to treat it.

  5. My 5 year old established pond has a sprayed in liner, bottom drain, skimmer and biofilter plus waterfall, 1000 gallons. I had koi in it until a month ago. Right before rehoming the koi I used Melafix to treat the koi after spawning. The water was foamy, so once they were gone I did a 75% water change and got 7 small goldfish. This was a month ago. The water was still foamy so I have done two more 50% water changes, one every two weeks. With the last one I expected no foam a clear water, but instead I have even more foam and cloudy water. Why? It tests fine. No debris on bottom, but polyfil is filtering out mud and I have no idea why since it was crystal clear before water change. Thank you. Great post btw.

  6. I have a well established pond but very cloudy water, has really had little maintenance over the last 5 years (previous owners). I have recently (2weeks ago) replaced the filter and UV as the UV unit was dead . This weekend we vacumed the pond and currently reduced the water by about 60%. I haven’t topped up the pond yet as i wanted to ensure we clear the brown colour water plus i thought best to get the new filter established. The water from the filter system is not clear (murky looking). Fish appear to be ok but I’m looking for advice on how i should move forward. Should i top up the pond and let it get established again then look at tackling the murky water.
    Regards Bob

    • Hi Bob,

      Massive apologies for such a delayed response! Any update on the status of your pond?

      The steps that you took are good, and it could be that the murky water is suspended sediment that just needs to settle. Have you tested your water quality parameters? Water hardness, salinity, pH, dissolved oxygen levels, and potential runoff all impact the health and appearance of your water. I would suggest refilling the pond, cleaning out the filter about once a week and performing partial water changes once a week (changing out 25-50% of the water and replacing with fresh). In addition, if there aren’t any plants in the pond I would highly suggest incorporating some, as these will help naturally filter the water and add in helpful nutrients and dissolved oxygen, as well as provide valuable habitat for your fish. We have a plethora of articles on all manner of pond plants; in particular, you may be interested in our article on oxygenating pond plants that can be found here:

  7. I built a Bigger pond for my koi fish that I’ve had for almost two years. I built a 1500 gal pond. I ran the pond with beneficial bacteria for three days before adding my koi. The water was clear. I transferred my koi from the old pond to the new pond and within 12 hour the water was murky and cloudy. Any reason for this. Thanks in advance for the quick response

    • Hi Joey,

      The most likely cause is that the addition of fish resulted in more ammonia and other waste products being released into the water. In turn, the beneficial bacteria are ramping up their numbers to consume this waste, and it’s causing the water to appear cloudy. This should resolve in a couple of days on its own, once the bacteria and nutrient levels sort of balance out.

  8. Hi, I’m after some advice please, I have built an new fishpond and have added the plants etc, also pebbles (as an after thought). I washed them first… but obviously not enough because now the water is cloudy and I’m worried that the debris (sand from the pebbles) will harm my fish. Can anyone please help?
    Thank you, Lou x
    Ps, I have yet to add the fish but need to do it ASAP.

    • Hi Louisa,

      That’s a strange one! I’ve personally used pebbles myself in many ponds throughout the years and have never experienced any problems with water clarity when using them.

      I’d hazard a guess here and say the cloudy water is very likely just the result of your new pond becoming established (natural beneficial bacteria growth, nitrogen cycle starting up etc.) and should clear naturally with time. New ponds tend to go through a transition period before they become more stable (and clear!), which often includes cloudy and murky water. Id say give the pond a few weeks or months and see how things settle.

      If you want to add fish, you could also perform a water quality test to ensure your pond water is within safe parameters. Cloudy water is very rarely dangerous to fish, but performing water quality tests is still a good habit to get into as it allows you to keep an eye on the health of the eco-system and catch problems in advance:

      If you’re still seeing cloudy water in a few weeks/months, please let me know your water quality test results and I’d be happy to try to advice further!

    • Hi. I’ve done exactly the same with my pond. Added pebbles (safe for fish) and did clean them as instructed first, but the pebbles dirt seems unlimited and every time it rains it -ours into my pond. I have emptied the pond once, but its happeded again. I, wondering if I leave it long enough dirt in the water will eventually fall to the bottom of the pond and clear. Did yours clear at all?

  9. Hi, I just built a new pond for my koi. I let the concrete dry for 3 days (very sunny in the Philippines) and then add water for another week with acid to neutralize the basicity of the cement. I rehome my kois without cycling the pond first because the previous pond was leaking. 1 week after, my water is iced-tea in color and it is almost dark. Is this a normal part of the pond balancing itself? Or should I be worried. I have not tested my water but the koi are pretty active.

    • Hi Kim,

      It could just be the pond working to balance itself. I would definitely suggest doing a water quality test to see what your parameters are, and then we can go from there on potential solutions! One thing you can do without knowing the parameters, though, is add some beneficial bacteria. Even if your parameters are normal, these won’t harm anything. They might be able to help clear up the water by eating any bacteria and waste introduced by your fish or other sources. Also adding in aeration and filtration, if you don’t already have those in place, will likely help.

      You can also conduct an experiment by simply dunking a glass or jar in the pond. After 24 hours, check on the glass and see how the water looks. If it’s still brown, it could just be tannins that are in naturally in the water. If the brown settles to the bottom, it’s more likely sediment or waste buildup from the ecosystem being imbalanced.

      Regardless, do check your water quality and get back to us!

  10. I have a rubber liner pond. The last few months when I get in, the bottom has a soft hairy carpet of black green algae, How can I get rid of it!

  11. I have a pond that is approximately 80′ x 40″ elliptical in shape about 2′ to 3′ deep along the perimeter to 6′ to 8′ in the center. One side had 3’± high field stone wall that was failing so we replaced it with large rectangular boulders. An excavator was used to remove the field stone and to level the base and place the boulders. In the course of doing so, buckets of clay soil were dumped into the pond so it now (three weeks later) looks like coffee with extra cream. It has changed very little in the three weeks. What can I do to settle the clay out of the water. There are approximately 300 Koi ranging from small to 20″± in the pond 20 year old pond.

  12. Hi having problems with a new pond. After putting in some plants, the peat/soil compost they are in keeps muddying the water. How do I stop this happening?

    Many thanks


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