Easy Fixes for a Cloudy Fish Tank

Published December 23, 2020
Man pumping out water to clean up the substrate in his aquarium

Sometimes fish keepers must decide how to manage a cloudy fish tank. There are a few main reasons water in the tank may look slightly foggy and unclear. Typically, when new hobbyists see little bits floating around the tank, they notice the problem and panic, but there are easy ways to prevent this problem.

Cloudy Fish Tank

When fish keepers overfeed or overstock their tank, it may create foul water and increase disease risk. Pet owners may not realize there is a problem until they see a few dead fish. If you have an established aquarium, there are a few essential steps to follow.

Remember that poor water conditions have a significant effect on your fish's regular feeding habits. Hobbyists need to pay close attention when the water is cloudy.

Foggy Cylinder Fish Tank

Why Is My Fish Tank Cloudy?

There are many reasons the water in your tank may be cloudy. Too much food can build up, and high concentrations of bacteria cause the aquarium's water to look milky. Dead fish may be a reason, so always look for fish at the top of the tank or behind rocks and plants. Check around!

Bacterial Bloom

An increase in the nutrient levels causes ammonia and nitrite levels to spike, and a bacterial bloom occurs. Ammonia and nitrite spikes can be deadly for your fish. The bacteria are suspended in the water, creating cloudy water.

Dirty Substrate

New substrates, including gravel, can cause cloudy water. The general rule of thumb is to always clean your substrates anytime you set up a new aquarium or clean an established tank. Sometimes filtration doesn't take out as much debris from the tank, and you end up with cloudy water.


New fish keepers often make the mistake of adding too much food. The food sinks to the bottom of the tank and starts to decay. Hobbyists need to stick to a strict feeding schedule.

Feeding goldfish in the aquarium at home

Too Many Fish

If you overstock your aquarium, the fish move around the substrates and disturb the water. Too many fish in a small tank causes the water to look milky.

Biofilm Forms on the Glass

Bacteria produce a biofilm that gives the glass a cloudy appearance. So it is not the water. It is the tank that's the issue. Use an algae scraper on the viewing pane of the fish tank.


Inadequate filtration can also be a problem. If the filter is too small for the fish you have, it can lead to cloudy water. Check if your filter is trapping all the items coming from the water.

Teenager cleaning gravel in a fish tank with a siphon pump

Top Ways to Prevent Cloudy Water in a Fish Tank

Proper fish tank maintenance is vital. Regular water changes are essential to keep your fish healthy. Also, get out the gravel vacuum and clean your substrates. The vacuum will pull out some of the fish waste and uneaten food.

  • Use proper water changes that replace 25 to 50 percent
  • Gravel vacuum the fish tank
  • Clean the glass with an algae scraper
  • Decrease the amount of food
  • Don't add more fish to the tank
  • Change the filter media often
  • Use a quality water test kit for the basic water parameters: pH, KH, ammonia, nitrite, and nitrate

Avoid a Cloudy Tank

Cloudy water in an aquarium is frustrating and can be an indication of a problem with your tank. Dead fish are a major red flag to change the water, vacuum the substrates, and check the aquarium pH with an at-home water test kit. Fish keepers with an established tank need to take proper care of the aquarium as even overfeeding can foul the water and increase the risk of disease.

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Easy Fixes for a Cloudy Fish Tank