Cloudy Fish Tank: Causes And How To Fix It For Crystal Clear Water

For many aquarists, the appearance of cloudy water in their tank is cause for alarm, especially if you haven’t a clue what could be the cause. In this article, we will look at some of the common causes of the unclear haze in tanks. Cloudy aquarium water can appear in a white, green, yellow, or brown color for many different reasons.

White Cloudy Water

This barely visible milky haze can be greyish, and sometimes it looks more like milk than water. Forgot to wash your substrate before adding it to your aquarium? You could end up with cloudy water within two hours of adding the substrate.


Gravel and sand substrates contain extremely fine specks that are created when they rub together. These end up as dust-like tiny pieces that you barely notice. Adding them to water separates them from the larger pieces of the substrate, and they float around your aquarium because they are so fine. The result is a visible, unsightly haze.

Water Changes

A water change is a good starting point as it helps to remove a good amount of the floating dust and detritus around your aquarium. You can change as much water as needed. However, a bit of patience as your filter continues to clear the water is the way to go. A fine mechanical media, such as filter floss, will eventually get rid of most of the floating dust.

Water Clarifier

To speed up the process, you can use a good water clarifier. A clarifier binds up the fine particles and enables the filter to trap them.

Gravel Vacuum Cleaner

Any amount of remaining dust can be easily removed from the floor of your tank where it is likely to settle. A gravel vacuum cleaner will clean up this dust quickly.

Bacterial Bloom

 Bacterial bloom is a common occurrence when setting up new aquariums. During the early stages of the tank cycling process, beneficial bacteria build-up to consume the ammonia being produced, which causes the water to turn milky.


Cloudy water during a bacterial bloom is a result of the strong growth of free-floating bacteria in the tank. This is quite normal.


 Patience and keeping things simple is what can help at this point. Avoid changing the water at the early cycling stages, as this removes the food and ammonia necessary for supporting the ecosystem that is trying to balance and establish itself.

For new aquariums, don’t introduce fish into the tank first. Set it up with filters and an air pump, add the water, add a water conditioner to remove chlorine, and then leave it for a while. Feed the tank and the filter just as you would if you had fish in the tank. If your water gets cloudy a few weeks later, which is likely, don’t worry. It will clear by the sixth week and you can then add the fish.

If the cloudy water turns green, which can happen sometimes, it is an indication that algal bloom has developed.

A sudden bacterial bloom can occur in an aquarium that has been running for a longer time. One reason why this can happen is seasonal changes. Temperature changes during the hot months or long periods of exposure to daylight can create a friendly environment for bacterial bloom.

Avoid setting up the aquarium in a place with too much exposure to daylight, and don’t leave your tank lights on for more than 6 to 8 hours every day.

You can temporarily use a UV purification unit to control the microorganisms and bacteria.

Green Cloudy Water

Green aquarium water is caused by millions of tiny pieces of algae that are small (microscopic). They become visible when they come together in large numbers and turn your aquarium a slight hazy green. As they grow in numbers, they turn your aquarium water into a cloudy green pea soup. The water may also take on a yellowish-green color depending on the plants and animals in your aquarium.


Generally, too much light, nutrient imbalance, and poorly maintained aquariums are the main causes of green cloudy water.

Phytoplankton is a plant, and is the cause of green cloudy water as well. Like most plants, it thrives very well in abundant light. The use of strong aquarium lights or keeping lights on for too long will encourage green aquarium water.


Reducing the amount of light that your aquarium receives is a simple and effective step that can stop green water from appearing in your aquarium. Avoid locations that can expose your aquarium to direct sunlight, such as near windows, and keep your curtains down.

Daphnia water fleas are very efficient as natural algae cleaners in tanks.

Balance Your Nutrients

Using too much or too little of a nutrient could encourage green aquarium water. Algae is a plant that competes with the others planted in the tank, and when a nutrient imbalance occurs, it is very possible to create conditions that favor the growth of algae, often without even realizing it.

Check Your Water Conditions

Use a water testing-kit to constantly check your water parameters. You’ll be able to notice unusual fluctuations in CO2 levels and can add liquid carbon if it is low. If phosphates, ammonia and other nutrients are out of sync, you can take preventive and corrective action.

Maintain Your Aquarium

Keeping a regular maintenance routine is one of the basic steps. You can do the following to remain on track:

  • Regular water changes
  • Clean your filter
  • Check your water parameters
  • Clean your gravel/substrate with a gravel vacuum
  • Avoid overfeeding
  • Remove uneaten fish food

Yellow And Brown Cloudy Water

Yellow and brown cloudy water is typically the result of plant matter in the water.


If you have driftwood in your aquarium, it could cause a change in the color of your water. Driftwood contains substances called tannins, which are natural dyes. Leaves or pods can also be the cause of tank water clouding. When immersed in water, the tannins slowly leach from the wood. Malaysian driftwood, for example, turns tank water brown. The colors are harmless to fish.


Simply immerse the trunk or wood in water for a while beforehand. You can use a separate container that is big enough and let it rest for a few days. This will release most of the tannins, and you don’t have to worry about them clouding your aquarium. You can then place your fish into your tank.


Sometimes, there could be more than one reason causing cloudy aquarium water in your tank. Simple routine maintenance eliminates most of the problems and makes it easier to identify and deal with cloudy water.