White cloudy water in a new tank is usually a harmless bacterial bloom that clears by itself in a few days to two weeks. Green water is algae (too much light), brown is tannins from wood, and grey right after setup is gravel dust. Test ammonia first: if it is up, change water.
What colour is it?
| Looks like | Usually | Fix |
|---|---|---|
| Milky white, new tank | Bacterial bloom | Wait; feed less; test ammonia |
| Grey, right after setup | Gravel dust | Settles in a day; rinse gravel next time |
| Green | Algae bloom | Cut light to 6–8 h; no direct sun; water changes |
| Tea brown | Tannins from wood | Harmless; carbon or water changes |
Don’t
Don’t add chemical clarifiers before you know the cause, don’t replace the filter media, and don’t overfeed: uneaten food is the most common fuel for cloudiness.
Questions
Should I do a big water change for a bacterial bloom?
Only if ammonia or nitrite is up. Otherwise, wait, feed lightly, and don't clean the filter; the bloom usually clears on its own.
Are tannins from driftwood harmful?
No. They tint the water like tea and slightly lower pH. Carbon in the filter or water changes clear them if you don't like the look.
General information, not veterinary advice. Updated November 2026.