Cloudy water right after adding guppies can feel like a disaster, especially if you were proud of how clear the tank looked. The good news is that cloudiness often has simple causes. The trick is identifying which type you’re dealing with, because the fix is different for each. Most cases are either a bacterial bloom, stirred debris, or a nutrient spike from overfeeding.
Type 1: Bacterial bloom (milky or hazy white)
This often happens in newer tanks or after a big change. Bacteria multiply in the water column when there’s excess dissolved organics. It usually clears on its own as the tank stabilises.
- What to do: feed lightly, avoid deep cleaning, and keep oxygen high.
- What not to do: don’t replace filter media (that removes the stabilising biology).
Type 2: Debris cloud (particles you can see)
If you disturbed substrate, moved decor, or added new sand/gravel, you may see fine particles floating. This is mechanical, not biological.
- What to do: use filter floss, reduce flow that stirs the bottom, and let the filter catch it.
- Extra tip: point the outlet away from the substrate so it doesn’t keep lifting dust.
Type 3: Nutrient haze (often paired with algae)
Overfeeding after adding fish is very common. Extra food dissolves and fuels blooms. This can look like haze and can develop into algae issues if light is high.
The “safe default” response
- test ammonia and nitrite (anything above 0 needs action)
- feed smaller portions for a week
- increase aeration and surface agitation
- do consistent moderate water changes rather than extremes
Cloudy water is usually a sign the system is adjusting. Keep the tank stable, don’t overreact, and you’ll often see clarity return within days once the biology settles.
