Test ammonia + nitrite + nitrate. Detectable ammonia or high nitrate (>40 ppm) suppresses appetite. Fix: 50% water change.
New fish often refuse food for 3-7 days while acclimating. Normal. Continue offering varied foods, dim lights, minimize disturbance.
Carnivores (mandarins, seahorses) reject pellets. Picky eaters (some clownfish) refuse foods they didn't see as juveniles. Try frozen mysis, brine shrimp, live foods.
Aggressive species eat first + stress others. Watch feeding times - if one fish always loses, separate or rearrange.
Loss of appetite is often the FIRST symptom of disease. Watch for white spots, fungus, fin damage in following days.
Cold fish slow metabolism + skip eating. Warm fish over-eat then crash. Verify temperature in species range.
Test water first - many "behavior" issues are actually water-quality problems. Use the water parameter checker to score your test results, the disease symptom matcher if you observe physical signs, or the general diagnoser to narrow further. Browse the full disease database if illness is suspected.
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