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

How to Clear Cloudy & Murky Water in Garden Ponds 2018 (Top Methods)

Cloudy water can make it difficult to see fish, and could be a symptom of a growing water imbalance.

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 effect mature ponds, too.  Common causes of cloudy water include bacteria blooms, excess nutrients, algae growth, tannin, 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.


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 eco-system 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 is needed to breakdown 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 buildup in the pond, the water becomes more and more murky in color and appearance.

4) Nuisance Algae Growth

Murky water that also looks a little green is likely caused by nuisance algae growth. As algae grow they leak tannin (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

Water test kits can provide a range of measurements and may help determine the cause of cloudy water.

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 un-cycled fish pond means there is no effective means of removing waste, so ammonia begins to rise. For mature ponds, it could be a combination of different things, and it would be impossible to pin-point the cause without further testing.

The best way to determine if you have a problem with water quality which 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

Extra fine polywool can be used to remove very fine debris regular filter media cannot remove.

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 optimised 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 polywool, is a great way to remove very fine debris and tannin (color) from pond water. If you have a pressuized filter, it is better to add the polywool 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

Sludge can be removed easily with pond vacuums, or broken down with sludge remover products.

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

UV Clarifiers can remove all free-swimming algae, and should help improve a cloudy, green pond water.

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.

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 clairifer 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 ponds 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 ponds eco-system 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 pin-point, 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!

4 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

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