Recurring fish deaths almost always trace back to setup or husbandry, not bad luck. 1. Uncycled or mini-cycling tank. Test ammonia + nitrite + nitrate. If ammonia > 0 or nitrite > 0, you have a cycle problem. Solution: dose with detoxifier (Seachem Prime), do 30% water changes daily, add bottled bacteria (Dr. Tim's One and Only). 2. Wrong pairings. Aggressive fish stress + kill peaceful fish over weeks. Examples: tiger barbs with bettas, large cichlids with tetras, multiple male bettas. Audit your stock against compatibility charts. 3. No quarantine. Pet-store fish often carry ich, velvet, flukes, or bacterial infections. Add to display = entire tank infected. Solution: 30-day QT for every new arrival. 4. Undersized tank. Common goldfish in 10g, oscar in 30g, plecos in 20g - guarantees death. Tank size dictates parameter stability + behavior. 5. Water-change neglect. Skipping months of water changes lets nitrate hit 80+ ppm. Slow toxic buildup. Solution: 25-30% weekly. 6. Pet-store fish quality. Mass-bred guppies, mollies, dwarf gouramis often carry chronic disease - look for captive-bred specialty breeders or quarantine aggressively. 7. Temp/pH swings. Heater failure, broken thermostat, room temp drops. Use 2 thermometers + replace heater every 2 years preventively.
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