Treating Ich in a Reef Tank Without Killing Your Corals

You cannot treat ich in the main tank

This is the hardest truth in the hobby: copper, formalin, and most commercial ich treatments will kill your corals, clams, snails, and shrimp. There is no medication you can dose into a reef tank to cure ich safely. The fish has to come out.

The only two reef-safe paths

1. Tank Transfer Method (TTM). Move the infected fish to a bare quarantine tank every 3 days for 12 days total, alternating between two QT tanks. This works by physically separating the fish from the free-swimming theront stage of the parasite's life cycle, since the parasite can't survive long off a host.

2. Hyposalinity. Lowering specific gravity to 1.009 in a quarantine tank over several days stresses the parasite more than the fish. Requires careful, gradual adjustment — a fast drop will kill the fish, not just the parasite.

Why your main tank usually doesn't need treatment

If your display has been fish-only for 60+ days with no new additions, the parasite's life cycle has almost certainly already collapsed — Cryptocaryon can't survive indefinitely without a host. The real risk window is the 2–4 weeks after introducing a new, unquarantined fish.

This is the single best argument for a dedicated quarantine tank: a $40 QT setup is cheaper than one round of ich tearing through a $2,000 reef.