Cloudy water is one of the most common worries for new fish keepers. The good news is that most cloudy water is not dangerous and clears up on its own once you know the cause. The color of the cloudiness is the best clue to what is happening.
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Quick Guide: What the Color Tells You
- White or gray haze: usually a bacterial bloom or dust from new gravel
- Green: free-floating algae, often from too much light
- Yellow or brown tint: tannins from driftwood or leaves, which are harmless
- Cloudy with a bad smell: rotting food, a dead fish, or a filter problem. Act quickly
White or Gray Cloudy Water
Bacterial Bloom
A milky white haze in a new tank, or after a big change such as a deep clean, is usually a bacterial bloom. Free-floating bacteria multiply quickly when there is extra waste in the water. It often clears on its own within a few days to two weeks as the tank settles. Our guide to cycling a fish tank explains why this happens.
What to do:
- Test for ammonia and nitrite. If either is above 0, do a partial water change
- Feed lightly, once a day, and remove uneaten food
- Do not do huge water changes or deep clean the filter, which can make it worse
- Do not keep adding chemicals. Give it time
Dust From New Gravel or Sand
If the tank went cloudy right after you set it up, fine particles from the substrate are a likely cause. Rinsing gravel well before adding it prevents most of this. Most dust settles or is caught by the filter within a day or two. Adding filter floss to the filter can help catch fine particles. See our guide to aquarium substrates.
Green Cloudy Water
Green water is caused by tiny algae floating in the water. It usually means too much light, especially sunlight, and extra nutrients. Cut the light to 6 to 8 hours a day, keep the tank out of direct sun, and feed less. A “blackout” of 3 to 4 days with the lights off and the tank covered often clears it. An aquarium UV sterilizer is also very effective. Read more in our guide on how to get rid of algae.
Yellow or Brown Water
Tea-colored water usually comes from tannins released by driftwood or leaves. Tannins are harmless and many soft-water fish like them. If you prefer clear water, soak new wood before using it, do regular water changes, and add activated carbon to your filter.
Other Common Causes
- Overfeeding: uneaten food breaks down and clouds the water. See our list of common fish feeding mistakes
- Overstocking: too many fish for the tank and filter
- A filter that is too small or not running properly
- Cleaning the filter media in tap water, which kills beneficial bacteria
- A dead fish or snail hidden behind decorations
- Some medications, which can cause temporary cloudiness
How to Clear Cloudy Water Safely
- Test the water with a liquid test kit for ammonia, nitrite, and nitrate
- Look for and remove any dead fish, snails, or rotting food
- Do a partial water change of about 20 to 25 percent using a water conditioner
- Vacuum the gravel with a gravel vacuum to remove waste
- Feed less for a few days
- Check that the filter is running and has enough flow
- Be patient. Most cloudiness clears within a few days to two weeks
When Cloudy Water Is an Emergency
Act right away if the water smells rotten, fish are gasping at the surface, or ammonia or nitrite is high. Do a partial water change, add an air stone for extra oxygen, and find the cause.
Should You Use a Water Clarifier?
Water clarifiers clump tiny particles together so the filter can catch them. They can help with dust but do not fix the cause of a bacterial bloom or green water. Use them only as directed, and never as a replacement for testing and water changes.
Final Thoughts
Cloudy water is usually a temporary sign that your tank is adjusting. Check the color, test the water, feed lightly, and give the tank time. Avoid the urge to fix it with big changes or lots of chemicals.
Have a question about your tank? Ask it in our friendly Facebook group, Beginners Fish Keepers, where new fish keepers help each other every day.
