How to Clear up Cloudy Water in Fish Tanks

Cloudy water can happen overnight in a fish tank, leaving the novice owner puzzled about what to do. Before heading back to the fish store for chemicals that can worsen the problem, change 25 to 50 percent of your water and wait a few days -- the cloudiness usually will clear up on its own.

Clown fish
Can't find Nemo in that murky tank? Infusoria may be the cause.
credit: Julialine/iStock/Getty Images

Causes of Cloudy Water

Cloudy water frequently happens two to three days after setting up a new aquarium. Microscopic organisms accompany the new fish in the aquarium water present in the plastic bags they ride home in. If your filter hasn't had time to produce bacteria to break down fish waste products efficiently, the tiny creatures proliferate. An established aquarium can develop cloudiness when a fish dies unnoticed in the tank, fish get overfed or the filter is not operating properly.

The Natural Solution

Determine why infusoria is proliferating in the tank and correct the source. Check that your filter is operating smoothly and change 25 to 50 percent of the water. Add good bacteria through seeding with live plants or items from an already established tank, such as a handful or two of gravel, a used filter pad or aquarium decorations. If you don't have access to an established tank, head to the fish store for a prepackaged culture or gravel infused with beneficial bacteria.