Likely cause
Green Water (Algae Bloom)
Green, pea-soup-colored water is a free-floating algae bloom, almost always caused by too much light (duration or intensity) combined with excess nutrients. Cutting back light hours helps prevent it from returning, alongside a direct algae treatment.
Why this happens
- Too much light — either duration (more than 8-10 hours a day) or intensity — feeds free-floating algae directly.
- Excess nutrients from overfeeding, overstocking, or infrequent water changes give algae more to consume.
- Direct sunlight hitting the tank is a common, often overlooked trigger.
What to do next
- Cut back lighting to 6-8 hours a day — a plug-in timer keeps this consistent — and move the tank out of direct sunlight if possible.
- Reduce feeding and do a partial water change to lower excess nutrients.
- Treat with an algae control product to clear the current bloom faster.
- Add fast-growing live plants if you want a longer-term fix — they compete with algae for the same nutrients.
- For recurring blooms, a UV sterilizer clears free-floating algae directly as water passes through it.
Frequently asked questions
How do I get rid of green water in my fish tank?
Cut back light exposure, reduce nutrients with a water change and lighter feeding, and use an algae treatment to clear the current bloom — then keep light and feeding in check to prevent it returning.