How to Quarantine New Fish

Ask experienced fishkeepers about their worst tank disaster and many will tell you the same story: one new fish brought in a disease that spread through everything. A simple quarantine tank prevents most of that. It's the habit that separates people who lose fish often from people who rarely do.

What a quarantine tank is

A small, separate tank where new fish live for a few weeks before joining your main tank. It doesn't need to be pretty:

• A 10- to 20-gallon tank, depending on the fish
• A filter that's already cycled: keep a spare sponge filter running in your main tank so it's ready when you need it
• A heater if the fish need one, and a lid
• A hiding spot (a pot or PVC pipe) to reduce stress
• Bare bottom or a thin layer, so you can see waste and keep it clean

How long

Many aquarists quarantine for two to four weeks, with longer for fish from uncertain sources. The goal is to give hidden problems time to show up.

What to watch for

• White spots like grains of salt (ich)
• Clamped fins, rubbing on objects (flashing)
• Ragged or rotting fins
• Cottony patches
• Not eating, hiding constantly, rapid breathing
• Thin, sunken belly despite eating

Treat in quarantine, not the main tank

If a problem shows up, you can treat it in quarantine without exposing the rest of your fish, plants or invertebrates. Remember that many medications harm shrimp and snails, and copper kills invertebrates. That's another reason to treat in a separate tank. Identify the problem first and follow the medication's directions.

Keep it clean

Use separate nets and buckets for quarantine, or clean them well between tanks, and wash your hands. Change water regularly; the small tank gets dirty fast.

Plants and invertebrates too

New plants can carry pest snails and hitchhikers. Rinse and inspect them, or quarantine them as well. See assassin snails for when pest snails sneak in anyway.

A few weeks of patience protects everything you've built. Your tank should also be fully cycled before anything new goes in.

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