Cloudy white — established tank
This looks like: ammonia spike and bacterial bloom triggered by extra waste — dead fish, overfeeding, or stalled biofilter
Why this happens
Mature tanks should not haze overnight without a trigger. Find the trigger — corpse, clogged intake, vacation feeding clicks.
What to do right now
- Test ammonia and nitrite — photo results.
- Hunt dead shrimp or fry behind wood; remove.
- Partial change 30% matched dechlorinated if ammonia >0.25 ppm — repeat until safe.
- Service filter intake/impeller without killing all biomedia — rinse in tank water.
- Cut feeding until water stays clean 3 days straight.
What not to do
- Don’t assume bloom is cosmetic — verify ammonia.
Stop it happening again
Don't overstock or overfeed, remove dead fish promptly, and keep up regular water changes so a mature tank never gets a waste spike.
If that doesn’t fix it
If tests stay perfect, rare pigment bacteria blooms exist — photo colour.
Catch this earlier next time — log your water parameters in App-aquatic. Free forever.
This isn't veterinary advice - it's a directional read to help you decide your next step, based on the most common causes. We can't see your fish, so pair it with a liquid test kit and clear photos, and see an aquatic vet or a trusted local fish shop for a valuable or seriously ill fish.