Post-water-change cloudiness has 4 distinct causes - patient diagnosis. Substrate stir-up (most common): agitated sand or fine gravel released into water column. Clears in 2-6 hours as particles settle. Crystal-clear by next day. Don't panic. Bacterial bloom: disturbing substrate releases dormant heterotrophic bacteria. They temporarily over-populate before nitrifiers stabilize them. Clears in 1-3 days. White haze with no other symptoms. Precipitation cloudiness: mixing cold tap water with warm tank water can precipitate dissolved calcium + carbonate as cloudy white particles. Common with high-KH water. Clears in 24h. Dechlorinator overdose: 5x dose of Prime can briefly cloud water. Clears in 2-4 hours. What NOT to do: 1) Another water change - chases the problem. 2) Add carbon (helpful but slow). 3) Add chemical "water clarifier" - polymer flocculants harmful to filter feeders. What TO do: 1) Wait 24-48 hours. 2) Test ammonia + nitrite to rule out cycle issues. 3) Reduce feeding for 2 days. 4) If smell develops or doesn't clear in 3 days = check for dead fish, snail, or filter problem.
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