Cloudy or green aquarium water: causes and fixes
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The short answer: cloudy white water is almost always a bacterial bloom, common in the first weeks of a new tank, and it usually clears on its own once the tank finishes cycling. Green water is a free-floating algae bloom, driven by too much light and excess nutrients. The fix is different for each: white cloudiness calls for patience, light feeding and steady water changes, while green water calls for cutting light, controlling nutrients and, if needed, a UV steriliser or a blackout. Chasing either with bottled clarifiers alone rarely solves the underlying cause.
Cloudy white or grey water
This is a bacterial bloom, a sudden growth of free-floating bacteria feeding on excess nutrients, most often in a brand new tank or after a deep clean. It looks alarming but is generally harmless to fish.
What to do:
- Be patient. In a new tank it typically clears within one to two weeks as the biofilter matures. Read our cycling guide below.
- Feed lightly and remove any uneaten food, which fuels the bloom.
- Keep up modest water changes. Test the water so you know where ammonia and nitrite sit; grab a kit from test kits.
- A fine mechanical polishing pad in the filter can pull out the haze. See filter media.
Green water
Green water is microscopic algae suspended in the water column, and it means the tank is getting more light and nutrients than the system can use. It is most common on tanks near a sunny window or with the light left on too long.
What to do:
- Cut the photoperiod back and move the tank out of direct sunlight. A timer helps.
- Reduce nutrients with water changes and lighter feeding.
- A UV steriliser, or a three to four day total blackout with the tank fully covered, will clear a stubborn bloom.
- Improve mechanical filtration, from our filters range, to help polish the water.
New tank, brown or dusty water
Brand new gravel or wood can leave dust or tannins in the water. Rinsing substrate before use and using a good water conditioner at setup helps. Tannins from driftwood are harmless and fade over time.
Fix the cause, not the symptom
Bottled clarifiers can clump particles so the filter catches them, but if the underlying cause, overfeeding, too much light or an immature filter, is still there, the cloudiness comes back. Solve the cause first.
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Come and ask us
Fishkeeping goes better when a real person can look at your setup. Come into the store in Lethbridge, call us at 403-380-4506, or send us an email, and someone who keeps fish will help you get it right. Written by the team at Tropical Fish Imports.