Cloudy aquarium water has several distinct causes - identify the color first. White or grey haze: bacterial bloom. Common in newly-set-up tanks (7-14 days post-setup) when heterotrophic bacteria temporarily overpopulate before nitrifiers take over. Don't panic - clears on its own in 3-7 days. Don't do massive water changes (slows cycling). Green water: single-celled algae bloom. Caused by too much light (especially direct sunlight), excess nitrate + phosphate, or a recent dechlorinator overdose that fertilized algae. Solution: 3-day blackout (cover tank, lights off), reduce photoperiod to 6-8 hours, do a 30% water change. UV sterilizer (9-13W) clears it overnight. Yellow tint: dissolved organic compounds (DOCs) from fish waste, decaying food, or driftwood tannins. Run activated carbon or Purigen for 2-3 weeks. Brown haze: diatom bloom (silica-fed). Common in tanks under 4 months. Clears as silicates deplete. Otocinclus and Nerite snails consume diatoms.
The full Q&A library answers the most-searched aquarium questions. Browse calculators, glossary, and disease database for related help.
Whatever specific topic brought you here, four fundamentals govern long-term aquarium success: water quality, parameter stability, biological filtration, and species-appropriate husbandry. Skip any one and the others struggle to compensate.
Water quality: ammonia + nitrite at zero, nitrate under 30 ppm freshwater + 10 ppm reef. Test weekly with API or Salifert kits. Use our water parameter checker to score your readings against your tank type.
Parameter stability: stable wrong parameters beat fluctuating ideal parameters. Most fish tolerate a wide pH range if it's stable. Sudden swings of 0.4+ pH or 5+°F kill fish faster than chronic suboptimal values. Use temperature controllers (Inkbird) + automated dosing for consistency.
Biological filtration: the bacterial colony on your filter media + rock + substrate is the engine. Never replace all media at once. Use our filter turnover calculator to size correctly.
Species-appropriate husbandry: research adult size, territoriality, diet, and tankmate compatibility before purchase. Use our tank stocking calculator + compatibility guides.
How long does an aquarium take to set up? 4-6 weeks for full cycling + first stocking. Use our cycle ETA calculator + how long does cycling take.
What's the best aquarium for beginners? 20-gallon long. Big enough for parameter stability, small enough for budget + space. See beginner picks.
How often should I do water changes? 25-30% weekly. See water change frequency Q&A + water change calculator.
Why does my fish keep dying? 5 leading causes: uncycled tank, wrong species pairings, no quarantine, undersized tank, neglected water-change schedule. See full diagnosis.
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