How to Quarantine New Saltwater Fish

🐠 The short version: a quarantine (QT) tank is the best habit in the hobby. Because you can’t safely medicate a reef, QT is where you watch a new fish for disease, treat it if needed, and keep parasites out of your display. It’s cheap and simple — a bare tank, a cycled sponge filter, a heater and a hide — and it protects everything you already keep.

🔧 Quarantine pairs with gentle acclimation on the way in and watching for ich and velvet while the fish settles.

Why quarantine is non-negotiable

Here’s the logic in one line: you cannot properly treat a reef display, so the only place to deal with disease is before a fish gets there. A quarantine tank lets you:

• Observe a new fish for a couple of weeks and catch disease early.
• Treat it in a bare tank where copper, hyposalinity and other methods can be used safely.
• Protect your display — one un-quarantined fish carrying velvet can wipe out a whole tank.

It’s strongly recommended for every fish and genuinely non-negotiable for ich-magnets like tangs.

Setting up a quarantine tank

QT is meant to be simple and functional, not decorative:

• A modest bare-bottom tank — easy to clean and to see the fish clearly.
• A cycled filter — a sponge filter or media seeded from your display, so there’s biological filtration from day one (a QT that isn’t cycled becomes its own ammonia problem).
• A heater and a lid (new fish jump).
• Hides — a couple of lengths of PVC pipe give the fish security and cut stress.
• The same salinity as your display (~35 ppt) unless a treatment calls for otherwise, matched on the salinity converter.

Keep it stress-low: dim, quiet, with hides. A calm fish holds disease off better.

How long, and observe-vs-treat

Plan on a few weeks — often two to four — long enough to observe through a disease cycle and finish any treatment. The fish is ready for the display when it’s eating well, behaving normally, and showing no signs. Ich-prone species and any symptomatic fish earn the longer end.

There are two honest philosophies, and either beats skipping QT:

• Observation-only: watch, and treat only if disease appears.
• Prophylactic: treat preventively (commonly for ich and flukes) on the assumption new fish carry something.

Which you choose depends on your risk tolerance. For any medication, follow the product’s instructions or an aquatic vet — this guide is husbandry, not a prescription.

What to watch for

While the fish settles, watch for the red flags (from our care-sheet vet-flag sections): white salt-grain spots (possible ich), a fine dusty sheen with rapid breathing (possible velvet — act fast), flashing/scratching, clamped fins, hiding, or refusing food. Spot something and you’re now dealing with it in QT, exactly where you can — see marine ich and velvet: what to do.

Corals and inverts, too

Corals and inverts don’t carry fish parasites, but they bring their own hitchhikers — flatworms, aiptasia, nuisance crabs. A separate observation period, plus a coral dip for corals, keeps those pests out of your display. (Never expose inverts to copper.)

The honest takeaway

A bare tank, a sponge filter and a few weeks of patience is the cheapest insurance in reefkeeping. Quarantine every fish, watch it settle, deal with anything there — and your display stays the healthy, stable tank you built.

Sources & further reading

• Coralkin — Marine ich and velvet: what to do — the diseases QT is protecting you from.
• Coralkin — Your first saltwater fish and Health questions.
• WetWebMedia — marine quarantine and disease references.
• Noga, Fish Disease: Diagnosis and Treatment and WAVMA — aquatic-veterinary guidance.