Fish get sick in every reef tank. The best outcomes come from fast, calm action. This guide helps you choose meds and use them safely.
Step 1: Diagnose first, then pick the right medication
Start with a quick checklist. Look for spots, dust, frayed fins, fast breathing, and flashing. Note appetite and hiding behavior. Test water before you medicate.
Bad water can mimic disease. Keep ammonia and nitrite at 0 ppm. Keep nitrate under 20 ppm for most reefs. Match salinity at 1.025 to 1.026. Hold temperature at 77 to 79°F.
Use a hospital tank for most meds. A 10 to 20 gallon tank works for small fish. Add a heater, lid, and air stone. Use a sponge filter seeded for at least 7 days.
Match symptoms to likely causes. White grains like salt often mean ich. Fine gold dust often means velvet. Stringy poop can mean internal worms. Red sores can mean bacterial infection.
- Ich: white spots, normal appetite early, slower course
- Velvet: dusty sheen, very fast breathing, rapid decline
- Flukes: flashing, cloudy eyes, excess mucus
- Bacteria: fin rot, ulcers, swelling, popeye
Do not mix medications “just in case.” Many combos stress fish. Some meds reduce oxygen. Always add extra aeration in treatment tanks.
For deeper setup help, see our quarantine tank setup guide. It covers filters, hiding places, and transfer tips.
Core meds and how to dose them safely
Copper treats ich and velvet in fish-only systems. Use chelated copper at 2.0 to 2.5 ppm, if the label allows. Raise the dose over 48 hours. Test copper daily with a matching test kit.
Keep copper stable for 14 days for velvet. Use 30 days for ich, when possible. Remove carbon and phosphate media during copper. Never use copper in a reef display. It can harm inverts and rock.
Praziquantel targets flukes and many worms. Dose per label in a hospital tank. Run it for 5 to 7 days. Repeat once after a 25% water change. Watch for appetite drops in wrasses.
Antibiotics help fin rot and ulcers. Use them in a bare hospital tank. Maintain strong aeration. Many antibiotics lower nitrifying bacteria. Test ammonia twice daily and use an ammonia binder if needed.
- Increase surface agitation during any treatment
- Check pH daily in small hospital tanks
- Feed lightly to control ammonia spikes
- Remove UV and ozone during medication
Freshwater dips can confirm flukes. Use dechlorinated RO or tap water. Match temperature and pH as close as you can. Dip for 3 to 5 minutes while observing closely.
Need feeding support during treatment? Read our reef fish feeding basics article. It includes recovery diets and vitamin options.
Troubleshooting, common mistakes, and reef-safe alternatives
The most common mistake is treating the display tank. Many “reef-safe” cures only mask symptoms. Parasites often remain in the system. A fallow period is usually required for true control.
If you see heavy breathing, act fast. Add an air stone and point a powerhead up. Lower temperature to 76 to 77°F if safe. Check for ammonia and correct it first.
Do not stop treatment early. Symptoms can fade before parasites die. Finish the full timeline. Keep notes on dates, doses, and test results. This prevents under-dosing and relapse.
Use supportive care in the display. Improve nutrition and reduce stress. Offer nori daily for tangs and angels. Add frozen foods soaked in vitamins 3 to 4 times weekly. Keep lights dim for shy fish.
- Example: Ich shows up after a new tang. Move all fish to copper for 30 days.
- Run the display fallow for 45 to 76 days, based on risk tolerance.
- Example: One clown flashes with cloudy eyes. Dip and treat with praziquantel.
For planning a fallow run, see our fallow period reef tank guide. It includes timelines and stocking strategies.
Sources: Noga, E.J. “Fish Disease: Diagnosis and Treatment”; Colorni, A. & Burgess, P. marine ich research summaries; HumbleFish community disease protocols (general methodology).
Medication works best with a clear plan. Diagnose, isolate, and treat with tested doses. Keep oxygen high and water stable. Your fish will recover faster with consistent care.
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