Cloudy aquarium water

Cloudy water looks like a crisis. The fix depends on which cloud it is. Test ammonia first. If fish are gasping, that page is gasping, not this one.

The short version: why is my aquarium water cloudy?.

Milky / grey-white (bacterial bloom)

New tanks in the first weeks, or after overfeeding, or after you rinsed the filter in the tap. Heterotrophic bacteria explode when dissolved organics spike.

• Do not crash-clean all the media
• Feed every other day for a week, two minutes max
• If ammonia or nitrite is above 0, change water and do not add livestock
• Wait. Blooms often clear as the cycle settles

UV will clear the look. It will not finish a cycle.

Green soup

Algae in the water column, not a film on the glass. Too much light, too many nutrients. Cut photoperiod. Algae. Light hours. UV and a blackout can knock it down; the surplus will grow it back.

Dusty brown after you scaped

Sand and aquasoil fines. Settles. Floss helps. Rinse sand in a bucket next time until the water runs less opaque.

Persistent brown film on glass and sand in a new tank is usually diatoms. Wipe. It fades as the tank matures.

What not to do

• Daily clarifying slime without a test
• New cartridge + 90% change + new fish
• Adding fish “to eat the cloud” — they cannot eat a bacterial bloom

Cycle before stocking. Feed less than you think. Size the filter for the livestock: stocking, filter flow. If cloudiness lasts more than two weeks with rising ammonia, it is water quality, not décor.