Likely cause
Bacterial Bloom (Cloudy Water)
White or gray haze is usually a bacterial bloom — a sudden spike in the bacteria that feed on excess waste or uneaten food, common in new tanks or after overfeeding. It typically clears on its own within a few days; testing your water rules out a bigger issue in the meantime.
Why this happens
- A sudden increase in bacteria feeding on excess waste, uneaten food, or a recent substrate disturbance.
- Common in new tanks that are still cycling, or after overfeeding in an established one.
- Overcleaning the filter (rinsing media in tap water) can also trigger a bloom by killing off beneficial bacteria that were keeping waste in check.
What to do next
- Avoid the urge to do a large water change right away — it can prolong the bloom by removing the bacteria trying to stabilize things.
- Cut back feeding for a few days to reduce the waste feeding the bloom.
- Test ammonia and nitrite to rule out a bigger underlying issue.
- Let it run its course — most blooms clear within 3-7 days on their own.
Frequently asked questions
How long does cloudy tank water take to clear?
Most bacterial blooms clear within 3-7 days on their own once the excess waste feeding them is reduced.
Should I do a water change for cloudy water?
A small water change is fine, but avoid a large one — removing too much of the beneficial bacteria can prolong the cloudiness rather than fix it.