The Ich Outbreak That Took My Tangs And Why the Wrasse Made It Out Alive

My black tang stopped eating on a Tuesday. By Thursday I could see the salt-and-pepper dusting across his flanks that every reefer dreads, and by the following week he was gone along with my yellow tang, my Atlantic blue tang, and both of my storm clownfish. The only fish that made it through was my wrasse.

Quick answer: This was a marine ich (Cryptocaryon irritans) outbreak in my peninsula tank. Tangs and clownfish are among the most ich-susceptible fish in the hobby, while wrasses tend to have thicker mucus coats and more robust immune responses, which is likely why mine pulled through. Recovery meant pulling the surviving fish, running the display fallow for weeks, and committing to quarantine for every future addition — not just hoping the next fish is clean.

What losing four fish in a week actually looks like

It didn't feel dramatic at first. One tang looked a little off, hiding more than usual, scratching against the rockwork. I told myself it was normal skittishness after a water change. Two days later the spots were unmistakable fine white grains scattered across the body and fins, the classic sign of Cryptocaryon irritans attaching to the skin and gills. Once one fish in a tank shows ich, the parasite is already in the water column and on every other fish that shares that water, whether or not you can see spots on them yet.

The yellow tang went next, then the Atlantic blue tang. My storm clowns a pair I'd had for a while and genuinely loved watching work the rockwork together went from fine to gone in what felt like no time at all. Tangs and clownfish are both notorious for taking the hardest hits in an ich outbreak; their skin and gill structure gives the parasite an easy foothold, and the stress of an active infection on top of everything else in a reef tank tends to be more than they can absorb.

My wrasse never showed a spot.

Why did the wrasse survive when the tangs didn't?

Wrasses aren't magically ich-proof, but they're generally considered one of the more resilient fish families against Cryptocaryon. A thicker protective slime coat, a less exposed gill surface, and depending on species genuinely strong immune responses all play a part. It doesn't mean a wrasse can't carry the parasite or come down with it under enough pressure; it means the odds tilt in their favor compared to a tang or a clownfish in the same outbreak. I wasn't relying on that resilience going in I only found out it mattered after the fact, watching one fish sail through what took out four others.

How do you get rid of ich in a reef tank?

Once I'd lost the four fish, the priority shifted from saving them to making sure the wrasse — and anything I add later — doesn't go through this again. Cryptocaryon irritans can't survive indefinitely without a host, but its cyst stage can sit dormant in sand and rockwork for weeks longer than most people expect, so the two things that actually matter are removing every fish from the display and giving the tank enough time completely fishless.

That means:

Pull every fish, including ones showing no symptoms — a symptom-free fish can still be carrying the parasite. Run the display completely fallow (no fish at all) for at least six weeks if you can hold the tank at 80°F/27°C, or closer to ten to eleven weeks at normal reef temperatures, since some cysts hatch on a much longer timeline than the textbook version of the lifecycle suggests. Treat any surviving fish in a separate, bare quarantine tank no substrate, no live rock using either copper (dosed to a tested target and held steady for a minimum of three weeks) or hyposalinity at 16–18 ppt for the same duration. Never dose copper in a display tank with corals or inverts; it will kill them.

What I'm doing differently now

The uncomfortable truth is that most ich outbreaks trace back to a fish that went straight from the store to the display with no quarantine in between. I'd gotten lax about it told myself the fish "looked fine" at the shop, which tells you nothing about what's incubating under the skin. Every new fish now goes through a full quarantine period before it ever sees the display, minimum three to four weeks, longer if anything shows even a hint of spots or stress. It's an extra tank, an extra chore, and it is non-negotiable after watching what the alternative costs.

I also stopped assuming a healthy-looking fish means a healthy tank. If one fish in a system shows ich, I treat every fish sharing that water as exposed, not just the one with visible spots.

Where the tank is now

The peninsula display sat fallow for the full stretch before anything new went back in, and the wrasse came through quarantine clean. Restocking has been slow and deliberate this time new fish arrive one at a time, each one gets its full weeks in quarantine, and nothing goes in the display until I'm genuinely confident it's clean. It's a slower way to build a tank back up than I'm used to, but after losing a black tang, a yellow tang, an Atlantic blue tang, and both storm clowns in one stretch, slow is exactly the point.