Marine ich can move fast in a reef tank. Early signs can look mild. Spotting them early helps you save fish and avoid panic.
What marine ich looks like on fish
The classic sign is white dots like salt grains. Spots are often 0.3 to 0.5 mm wide. They show on fins first. They can also appear on the body and gills.
Do not trust spots alone. Ich can drop off within 24 to 72 hours. The fish may look “cured” for a day. That is often a false break between waves.
Watch behavior changes. Fish may scratch on rocks and sand. This is called flashing. Fins may clamp tight to the body. Appetite may drop during heavier cycles.
Gills can be the first target. You may not see spots at all. Look for faster breathing and hanging near flow. A resting tang that pants can be in trouble.
- Count breaths for 15 seconds, then multiply by four.
- Over 80 breaths per minute is a red flag for many fish.
- Check both sides of the fish for uneven gill movement.
Common early signs you can miss
Early ich often shows as dull color and stress bars. Fish may hide more than normal. They may stop competing for food. These are easy to blame on “new tank nerves.”
Look for a thin, dusty sheen under blue lighting. Some fish show a faint haze before spots. This can also suggest velvet. Velvet usually looks finer than salt.
Spot patterns matter. Ich spots tend to be fewer and larger. Velvet tends to cover more area quickly. Velvet also causes very rapid breathing and fast decline.
Use a simple log to avoid guessing. Note date, fish, and symptoms. Also note feeding response. This helps you see the cycle. It also helps in treatment planning.
- Take a quick phone photo each day under the same light.
- Record temperature, salinity, and pH at the same time.
- Mark any new additions from the last 30 days.
Confirming signs and first actions
Start with water checks. Stress makes outbreaks worse. Keep salinity stable at 1.025 to 1.026. Keep temperature steady at 77 to 79°F. Aim for pH 8.1 to 8.4.
Do not treat the display tank with copper. Copper can kill invertebrates. It can also bind to rock and sand. Instead, plan a hospital tank. Use a bare tank with PVC hides.
Move fish to quarantine if possible. Then treat with a proven method. Copper is common for ich. Many hobbyists target 2.0 to 2.5 ppm with chelated copper. Always follow your test kit range.
Leave the display tank fallow to break the life cycle. Many reef keepers use 76 days fallow for safety. Feed corals and inverts lightly during this time. Keep filtration stable.
- Increase oxygen with an air stone in quarantine.
- Keep ammonia at 0 ppm using daily tests and water changes.
- Review your quarantine tank setup before you buy meds.
Some mistakes cause repeat outbreaks. Adding “cleaner” animals will not cure ich. Relying on reef-safe cures often fails. Skipping quarantine is the biggest risk. See our fish quarantine basics and reef tank disease prevention guides.
If you are unsure, act early. Treating late is harder. Watch breathing, appetite, and behavior daily. Small changes often come before the spots.
Sources: Colorni, A. (1987) Biology of Cryptocaryon irritans; Noga, E.J. (2010) Fish Disease: Diagnosis and Treatment; Hemdal, J.F. (2020) Marine Fish Health & Feeding Handbook
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