The short answer
Strictly speaking, no — you can keep fish without one. But a quarantine tank is strongly recommended, and experienced hobbyists consider it one of the best habits you can build. It stops a single sick new fish from wiping out an entire established tank, and it gives you a calm space to treat illness without medicating your main display.
Why it matters so much
New fish are stressed from shipping and often carry parasites or bacteria that only flare up once they settle in. Drop them straight into your main tank and any disease spreads to every fish at once — plus you’d have to medicate a planted, stocked display, which is far harder. A 2–4 week quarantine lets problems surface and be treated in isolation.
Setting one up
A quarantine (or “hospital”) tank is deliberately bare and simple:
- A small tank or food-grade tub — 20–40 litres is plenty.
- A cycled sponge filter (keep one running spare in your main filter so it’s ready).
- A heater to match your main tank’s temperature.
- Somewhere to hide — a plant or a bit of pipe. No substrate needed.
Keep it easy to clean and easy to dose medication in.
When you can skip it
If you’re an occasional keeper adding one fish very rarely, some people risk it. But the moment you have an established, well-stocked tank, quarantine becomes worthwhile. See also do I need to quarantine new fish and how to tell if a fish is sick. For gear, browse our filter and heater hubs.