You did a water change last weekend, and by Thursday the tank looks like pea soup, tea or weak lemonade. The colour of your water is a clue. Each tint points to a different cause, and some are harmless. Here is how to read them.
Green Water
Cause: a bloom of free-floating algae, usually from strong light or direct sunlight combined with excess nutrients.
Is it harmful? The fish are usually fine, but a heavy bloom can use up oxygen at night.
What to do:
- Reduce lighting to 6 hours and block direct sunlight.
- Do a 25 to 30 per cent water change with water treated with Sunken Garden Anti-Chlorine.
- Feed less and test nitrate.
- If it stays, cover the tank for 2 to 3 days with the air pump running.
- Add fast-growing plants to use up nutrients.
Brown Water
Cause: one of three things. Tannins leaching from driftwood or almond leaves give a clear, tea-coloured tint. Diatoms form a brown dusty film on glass and decor in new tanks. Disturbed debris or decaying matter makes it muddy.
Is it harmful? Tannins are harmless and even mildly beneficial. Decaying waste is not.
What to do: pre-soak driftwood before use, wipe off diatoms; let the tank mature, and siphon out debris and uneaten food.
Yellow Water
Cause: tannins again, or dissolved organic compounds building up from overfeeding, infrequent water changes or decaying plant matter.
Is it harmful? It signals that waste is accumulating.
What to do: change 25 to 30 per cent of the water weekly, remove dead leaves and rinse filter media gently in tank water. Activated carbon in the filter removes the tint.
Quick Diagnosis Checklist
- When did the colour appear: after a water change, a new decor, or a lighting change?
- Is it clear but tinted, or cloudy? Clear and tinted is usually tannins. Cloudy or milky is a bacterial bloom, covered in our cloudy water guide.
- Test ammonia, nitrite and nitrate with TCWS Water Test Strips.
- Check how many hours the light runs and whether sunlight hits the tank.
- Review how much you feed.
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