cloudy aquarium

Why is My Aquarium Water Cloudy?

Everyone enjoys watching beautiful tropical fish swim and explore the aquarium. The swaying aquatic plants and interesting aquascape can make you feel like there’s a piece of an Amazonian river or African lake right in your own home. But cloudy aquarium water can give the tank a dirty, murky appearance.


The truth is, nearly all aquarists wrestle with cloudy water sometime, no matter how experienced they are. It can be very frustrating, leading some new aquarists to abandon the hobby.
The good news is cloudy water isn’t impossible to cure. But there are specific types of cloudy aquarium water, each with its own cause and cure. Fighting a cloud requires knowing what caused it. Otherwise it will keep coming back! Want to know more?
Here’s what you need to know to keep your aquarium sparkling clear!

Identifying the cause of cloudy aquarium water

The fist step in addressing a cloudy aquarium is determining what type of cloud is causing the issue.

Many aquarists can’t identify the substance that is causing murky aquarium water. This leads to frustration when attempts to clear up the water fail.
It’s possible to take drastic measures, like draining the aquarium, washing the gravel and ornaments, refilling the tank and having the cloud form again.
The slogan “knowledge is power” is especially true when trying to solve aquarium issues. You can spend a lot of time and money needlessly by misdiagnosing a cloudy water problem.
We’ll identify the various symptoms and causes of murky aquarium water, so you’ll know what is causing the problem in your tank.

What color is the water?

Before trying to fix a cloudy aquarium, it’s important to train yourself to mentally describe what the water looks like.
This is important because it will allow you to identify what is causing the unsightly water condition.
Here are the three main visual categories of cloudiness in the aquarium

  • Clear with a tint of color (green, brown, tan, yellow, etc.)
  • Clear with suspended particulates
  • Cloudy with a distinct color (green, white, gray)

It is possible to have “clear” water with a color tint. Imagine a glass of iced tea. You can see through the liquid, but it has a brown color.

“Cloudy” means the water has something suspended in it that obscures the fish, plants and reduces light penetration in the tank.

Some cloudy water is like pea soup. It’s so thick you may not even be able to see your fish! Now let’s take a look at each type of cloud and discuss what it is, what caused it and how to fix it.

Clear water with a color tint

The most common water discoloration, often described as a cloud, is water with a green tint to it.
Green water, as it’s called, is caused by millions of tiny green algae cells floating around in the water. The green algae, when in high enough numbers, will make the water have a greenish color. You can still see through the tank, but it looks swampy.
Here’s something to consider. Crystal clear aquarium water is teaming with algae cells. It’s only when they become so great in numbers, that they affect how you see your aquarium.
Water changes may help if you’ve got a build up of nutrients in the aquarium.
Dilution is a great way to stave the algae.
Over feeding can also stimulate the algae, causing a green tint to the water. Cut back on the amount and frequency of feeding. Uneaten food should never be seen in the aquarium. Keep the aquarium light on for no more than 10 hours.


The second most common discoloration is caused by a build up of organics in the water.
Algae, fish waste and other natural substances will accumulate in the water. They give the water a yellowish or brown tint, like weak tea.
It’s easier to see the color when the light is turned off and you look through the aquarium. Yellowish water is a sign that organics are accumulating in the tank.
A dirty aquarium with organics tends to be a “sick” tank. The neglected water quality affects fish health. Disease causing organisms thrive in organic rich aquariums. Dirty water increases the likelihood of disease problems.
Water changes along with a light siphoning of the gravel bed will dilute the organics. Using activated carbon to adsorb organics will keep the water crystal clear.
Be sure to change the activated carbon every three to four weeks.

Aquarium water with a reddish or pink tint is usually being over fed.
The colors used in the food formula will “bleed” out into the water, giving it an unnatural color. Brightly colored foods that are uneaten and decaying in the tank will cause this problem. While water changes will help, you must reduce feeding if it is the cause of this kind of “cloud” problem.

Clear water with suspended particles

If you’ve just set up your aquarium and added water, there is usually a slight cloudiness to the water. This is caused by residual dust on the gravel.
Colored or epoxy coated gravel are usually very clean. Natural sand, gravel and dolomite can be dusty and cause murky water.
In time the dust will settle.
An aquarium filter with fine mesh mechanical filtration sponges or fiber floss will help clear the water.

Sometimes a very dirty tank will suffer from floating particles. The tan or black debris are comprised of uneaten fish food, solid fish waste and bacterial slime.
Aquariums with a heavy fish load or large fish, like cichlids, can have this type of cloud problem.
A gravel siphon is helpful for removing solids on and in the gravel. You may need a more powerful aquarium filter to keep the solids suspended so they can be pulled into the filter. Remember to change the filter media frequently if there are a lot of solids in the tank.
If not, the organic matter will decompose inside the filter, releasing algae promoting nutrients into the water.

Cloudy water with a distinct color

A newly set up aquarium will go through a break in phase within a few weeks of adding fish. Bacteria that play an important role in recycling wastes often cause the water to turn murky white or gray color.

This is normal and will clear up in a week or so. If you’ve added too many fish all at once or add too much food, the cloud won’t clear up.
That’s because excess waste and feeding keeps the aquarium unbalanced. The tank conditions favor the bacteria, not clear water with a nice biological balance.
Some aquarists believe ammonia causes cloudy water. This is incorrect. Over feeding and over stocking cause the bacteria to reproduce so much the water is cloudy with bacteria.
Over stocking and over feeding can also cause a spike in ammonia and nitrite, which is unrelated to cloudy water, but can happen at the same time due to poor conditions in the aquarium.
Makes water changes and reduce feeding if this is your situation.

Thick, green “pea soup” is caused by green algae “blooming” in the water.
The algae cells are reproducing so quickly the water turns bright green. Too much light or having the light on for more than 10 hours can stimulate algae blooms.
But the algae also need nutrients to reproduce. If the water didn’t have enough nutrients, the algae could never grow and cause the pea soup problem. Cut back on feeding, make water changes and see if the algae clears.
Since the algae are reproducing, it’s hard to keep up with them sometimes. An algaecide may be necessary to bring the bloom under control. Try the natural approach of reducing nutrient input by limiting fish food for a week or two. If it does not work, an algaecide may be required.
We have an in depth article with tips to get rid of algae if you need more help.

A word on algaecides and water treatments

Algae problems usually can be solved using the methods we discussed. If not, algaecides can help.
While it is true algaecides don’t “fix” the root problem, they can often trigger the tank to self balance and clear up after one or two treatments. Follow the directions and don’t over dose!
You’ll also find water clarifying treatments. Some are formulated to grab onto algae cells and debris, clumping them into larger, heavier particles. The larger particles are easier for the aquarium filter to remove.
The important thing to remember is to change the filter media every day or two when using clarifiers. Once the filter media is full of debris, it can’t capture any more.
Frequent cleaning will improve the efficiency of the filter and make it easier to clear the water. Some treatments contain live bacteria. The idea behind bacterial cleaners is to digest solid waste and sludge build up in the tank. However, they can’t clear up al algae bloom or remove the organics that cause yellowish water.

Final thoughts on cloudy water

A temporary cloud is normal for new aquariums. Everybody experiences it. Just let nature take care of it.
Chronic discolored water is a sign of poor care or an imbalance of food, nutrients or organic waste.
Proper maintenance of the aquarium filter is very helpful. But for long-term health and stability of the aquarium, a proper balance of feeding and fish load must be achieved to keep the water clear.
Resist the urge to add more fish or another serving of food and you’ll find your aquarium water stays crystal clear!

Why is My Aquarium Water Cloudy?