Marine Ich (White Spot Disease): Identify & Treat

Marine Ich (White Spot Disease): Identify & Treat

What It Is Cryptocaryon irritans parasite
Looks Like Grains of salt on fins & body
Danger High — can wipe out a tank
Treatable Yes, in a bare quarantine tank
Reef-Safe Cure None — must treat in QT

Overview

Marine ich (Cryptocaryon irritans) is the most common fish disease in the hobby. It’s a parasite that shows as tiny white “salt grain” spots on fins and body. The tricky part is its life cycle: the visible spots are only one stage, and the parasite drops off to reproduce in the sand before reinfecting — so “the spots went away” does not mean it’s gone. Tangs, and stressed or newly-added fish, are especially prone.

Symptoms

Pinhead-sized white spots like grains of salt or sugar on the fins, body, and gills; flashing (scratching against rock); rapid breathing; clamped fins; and lethargy or hiding. Spots appear, then vanish as parasites drop off — then return in greater numbers a few days later. That come-and-go cycle is the signature of ich.

How to Treat It

    n

  1. Move fish to a bare quarantine tank — you cannot safely medicate a reef; the effective treatments harm corals and inverts.

    2. n

  2. Copper (at therapeutic level, monitored with a copper test) or the tank-transfer method (moving fish to fresh clean tanks on a schedule that outpaces the parasite’s life cycle) are the reliable cures.

    3. n

  3. Run the full course — treat for the complete recommended duration, not until spots disappear, because of the life cycle.

    4. n

  4. Leave the display fishless for around 76 days so the parasite starves out with no host, while treated fish recover in QT.

    5. n

Prevention

Quarantine every new fish — ich almost always rides in on a new arrival. Keep fish unstressed with stable parameters, good food, and no bullying; a healthy fish’s slime coat resists infection. A proper quarantine routine is the single best defense against ever seeing ich in your display.

Common Mistakes

“Reef-safe ich cures”: most don’t reliably work — there is no proven in-display cure; treat in QT. Stopping when spots vanish: the parasite is mid-cycle, not gone — finish the course. Not quarantining new fish: the reason ich enters a tank in the first place.

Related Guides

Why You Need a Quarantine Tank · Marine Velvet: The Fast Killer · Yellow Tang