| What It Is | A separate tank for new fish |
| Size | A simple 10–20 gallon works |
| QT Period | 2–4 weeks observation |
| Prevents | Ich, velvet, brooklynella, flukes |
| Golden Rule | Quarantine EVERY new fish |
Overview
A quarantine tank (QT) is the most important piece of “equipment” a reefer can own, and the most skipped. It’s a simple separate tank where new fish live for a few weeks before joining your display, so that any disease they carry shows up in isolation — where it’s cheap and easy to treat — instead of in your reef, where it’s a catastrophe. Nearly every wipeout story starts with “I didn’t quarantine.”
Why It’s Worth It
You cannot medicate a reef display — copper and most treatments kill corals and inverts. So if ich or velvet enters your reef, your only options are tearing every fish out to treat, or watching them die. A QT stops that at the door. It also lets you fatten up and settle a new fish, and treat for common parasites preventively, before the stress of a community tank.
Setting One Up
- A bare 10–20 gallon tank with a heater, a sponge filter (pre-seeded from your display for instant biology), and some PVC pipe for hiding places.
- No sand or rock — bare bottom is easy to clean and doesn’t absorb medication.
- Match temperature and salinity to your display for easy transfers.
- Observe new fish 2–4 weeks; treat if anything appears. Many hobbyists run a preventive copper or tank-transfer course regardless.
- Only move a fish to the display once it’s eating well and clearly healthy.
Common Mistakes
“This fish looks healthy, I’ll skip it”: ich and velvet incubate invisibly — healthy-looking is exactly how they get in. No seeded filter: an un-cycled QT spikes ammonia — keep a sponge filter running in your sump so it’s always ready. Treating the QT like storage: it’s observation and treatment, not a holding bucket — keep water quality up.
Related Guides
Marine Ich (White Spot Disease): Identify & Treat · Marine Velvet: The Fast Killer · Brooklynella (Clownfish Disease) · How to Acclimate New Fish
Frequently Asked Questions
Why do I need a quarantine tank?
It lets you observe and treat new fish for disease before they reach your display, preventing a single sick fish from introducing ich or velvet to the whole system. It is the cheapest insurance in the hobby.
How long should fish stay in quarantine?
Commonly 2 to 4 weeks of observation, longer if you are treating. A full prophylactic protocol runs several weeks to clear the major parasites before the fish joins the display.
What does a quarantine tank need?
Just the basics: a bare-bottom tank, a sponge or hang-on filter, a heater, a PVC hiding spot and a lid. No rock or sand, so medications like copper stay effective and are not absorbed.