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 a cause for alarm, especially if you do not have a clue about what could be the cause. Cloudy aquarium water can appear in white, green, yellow, or brown colors for many different reasons.

This article will look at some of the common causes of the unclear haze in tanks that can be worrisome.

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.

How so? Well, gravel and sand substrates contain extremely fine specks that are created when it rubs 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 since they are so fine. The result is a visible, unsightly haze.

How to fix white cloudy water

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. 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 much of the floating dust.

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. 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! Patience! and keeping it 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 a new aquarium, don’t introduce the fish into the tank first. Set it up with filters and an air pump, add water, add a water conditioner to remove chlorine and leave it. Feed the tank and the filter just as you would if you had fish in the tank. If your water gets cloudy in a few weeks, which is likely, ignore that. It will clear in four to six weeks, and you can then add the fish you want.

If the cloudy water turns green, as can happen sometimes, it is an indication that algal bloom has developed. Most likely caused by green water.

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 if they are low in numbers. 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.

Causes of green cloudy water

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

Too much light

Phytoplankton is a plant, and 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 time and 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.

Nutrient Imbalance

Using too much or too little of a nutrient could encourage green aquarium water. How so? 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.

By constantly checking your water parameters, you can notice unusual fluctuations in CO2 levels or phosphates and take preventive and corrective action.

Unmaintained aquariums

Keeping a regular maintenance routine is one of the basic steps that must never be neglected. Waste and decaying fish food,(from overfeeding)will accumulate and trigger all manner of avoidable complications.

You can do the following to keep on track.:

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

 Yellow and brown cloudy water

If you have driftwood in your aquarium, it could cause a change in the color of your water. Well, driftwood contains substances called tannins which are natural dyes. When immersed in water, the tannins slowly leach from the wood. Malaysian driftwood, for example, turns tank water to brown. Manzanita driftwood hardly releases any color. The colors are harmless to fish.

A simple solution for this is to boil the trunk or wood before placing it in the tank. That will release most of the tannins, and you don’t have to worry about them clouding your aquarium.


Sometimes there could be more than one reason at the same time 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 if it happens.