Saltwater Issues
Fish Flashing or Scratching
Symptoms
- Fish darting against rock, sand, or powerheads
- Twitching, rapid breathing, or clamped fins
- Sometimes visible white spots, gold dust, or mucus patches
Likely causes
- External parasites — marine ich (Cryptocaryon), velvet (Amyloodinium), flukes
- Ammonia or copper irritation
- Low pH or sudden salinity change
- Aggression from a tankmate causing stress
Immediate steps to take
- Observe under bright light — look for white salt-grain dots (ich) or fine dust (velvet)
- Test ammonia, salinity, and pH; correct any out-of-spec value gradually
- If parasites are confirmed, move affected fish to a bare-bottom QT and treat with chelated copper (1.75–2.5 ppm) or tank-transfer for ich
- Run UV sterilisation in the display to reduce free-swimming parasite load
Long-term prevention
- Quarantine every new fish for a minimum of 4 weeks with prophylactic copper plus prazipro
- Never add fish from a system you have not seen healthy
- Keep aggressive species (damsels, large angels) out of mixed-peaceful displays
- Maintain stable salinity (1.025–1.026) and pH (7.9–8.4)
Recommended products & practices
Once parasites enter a display, the only reliable cure is removing all fish for an 80-day fallow period while treating in QT. Prevention through quarantine is dramatically easier than treatment.