Most common parasite cause. Look for white salt-grain spots within 2-3 days of flashing onset. See /diseases/ich-saltwater/ or /diseases/ich-freshwater/.
Microscopic flatworms cause itching. Treat with PraziPro 7-day course in QT.
Gold/bronze dust appearance + rapid breathing + flashing. URGENT: copper treatment in QT.
Toxic water burns gills. Test water; flashing without visible spots may be water quality.
pH shock or salinity crash. Verify parameters match species needs.
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.
Browse all behavior troubleshooting articles.