Catch problems first
Ich, fin rot, and other problems often show up in the first couple of weeks after a move. You see them in a small tank, not in your display.
New livestock
Quarantine and Compatibility
New fish can carry parasites or disease that take days to show. A simple quarantine tank and a few compatibility checks protect the animals you already have.
Why bother
What quarantine protects
One sick new fish can spread a problem to the whole display. A few weeks in a separate tank is cheap insurance.
Treat a small tank
Treating a small tank takes less medication and keeps it away from your display, plants, and filter.
Rest after the trip
New fish settle in and start eating without competing with established, territorial tankmates.
Keep treatments away
Many treatments harm shrimp, snails, live plants, or coral. Quarantine lets you treat fish without exposing them.
What you need
A simple quarantine tank
It does not need to look nice. It needs to be stable, easy to clean, and easy to see into.
Small tank with a lid
A 10 to 20 gallon tank works for most small fish. Larger fish need a bigger tank.
- Use a lid: stressed fish jump
- Bare bottom so you can see waste and leftover food
- Keep it away from loud, busy spots
Cycled sponge filter
A sponge filter on an air pump is gentle, cheap, and easy to keep ready.
- Keep a spare sponge in your display filter or sump so it stays seeded
- Some medications can harm filter bacteria
- Test ammonia every day or two
Heater and thermometer
Hold the quarantine tank at the same temperature as your display so the final move is easy.
- Size the heater to the tank
- Use a thermometer you can read at a glance
- Saltwater: match the display's salinity too
Cover and separate tools
PVC pipe or a plastic plant gives cover without soaking up treatments the way rock and gravel can.
- Use a separate net, bucket, and siphon
- Wash your hands between tanks
- Saltwater: keep live rock out of quarantine
Step by step
Do these in order
Plan on about 2 to 4 weeks in quarantine. Many saltwater keepers quarantine longer.
Acclimate gently
Float the closed bag for about 15 minutes to match temperature. Then add a little tank water to the bag every few minutes for 15 to 30 minutes.
- Net the fish out and throw the bag water away
- Shrimp, snails, and most saltwater animals need a slower drip acclimation
- Keep lights dim for the first few hours
Watch every day
Check each fish closely at feeding time. Note anything new.
- White spots, frayed fins, or cloudy eyes
- Fast breathing, clamped fins, or rubbing on objects
- Not eating, hiding all the time, or stringy white waste
Treat only what you see
If a problem shows up, identify it before you treat. Use a treatment made for that problem and follow the label.
- Remove carbon while treating: it pulls out medication
- Copper treatments belong in quarantine, never in a reef tank
- Keep up water changes and ammonia tests
Wait, then move
Move fish only after they have eaten well and looked healthy for the whole quarantine period.
- If you treated, count the time again from when they recover
- Acclimate again into the display
- Never pour quarantine water into the display
Before you buy
Check compatibility
Quarantine cannot fix a fish that does not fit your tank. Check these four things before every purchase.
Plan for the grown fish
Most fish are sold young. Look up the size they reach, not the size in the store.
- Fast swimmers need tank length, not just gallons
- Big fish often eat anything that fits in their mouth
Peaceful or pushy
Mix fish with similar temperaments and swimming speeds.
- Fin nippers and slow, long-finned fish do not mix
- Schooling fish usually do best in groups of six or more
- Add territorial fish last
Same water, same food
Tankmates should want the same temperature, pH range, and hardness.
- Coldwater fish such as goldfish do not belong with tropicals
- Make sure each fish can get the food it needs
Reef-safe or not
Reef-safe means a fish is not expected to eat or nip coral and invertebrates. It is a guide, not a promise.
- Some reef-safe fish still eat small shrimp or snails
- Ask about each fish before adding it to a reef tank
Avoid these
Common mistakes
Most quarantine problems come from rushing or from a tank that was not ready.
An uncycled tank
A fresh tank with a new filter can spike ammonia. Keep a seeded sponge ready or test and change water often.
Cutting it short
A few days is not enough. Some problems take a week or more to show.
Sharing tools
A wet net moved from quarantine to the display can carry disease with it.
Guessing at treatments
Mixing medications or treating the wrong problem adds stress. Identify the problem first and follow the label.