Green cloudy water
This looks like: green water — single-celled algae bloom
Do this firstBlackout or cut photoperiod to 6 hours for a week — no siesta midday sun through window.
Why this happens
Light + nitrate/phosphate fuels bloom faster than plants can grab it. Tanks near sunny windows spike fastest.
How sure are we? Very high with neon-green colour and fine haze.
What to do right now
- Blackout or cut photoperiod to 6 hours for a week — no siesta midday sun through window.
- Continue small measured water changes; vacuum detritus.
- Add fast-growing plants or floating cover to compete for nutrients later.
- UV sterilizer helps if you already own one — otherwise blackout first.
- Check tap phosphate if old pipes or fertiliser dosing misfires.
What not to do
- Don’t blackout fish that need light for heat unless tem temp stable.
Stop it happening again
Keep the tank out of direct sunlight, run a sensible light period of six to eight hours, and don't overfeed - green water is light plus excess nutrients.
If that doesn’t fix it
Brown tint is different — tannins diagnosis.
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.