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Most disease in an established aquarium arrives with a new fish. The fish look fine in the store, but transport and handling stress them, and hidden infections break out a few days later in your tank.
Why fish that look healthy are not always healthy
The University of Florida’s guide to ich explains that newly arrived fish can be asymptomatic carriers that break with disease after transport and handling, and calls preventing this one of the most important reasons all incoming fish should be quarantined.
A simple quarantine setup
| Item | Why |
|---|---|
| A small separate tank | Keeps new fish apart from your main tank |
| Heater and thermometer | Matches the main tank’s temperature |
| Seeded filter | Media from the main tank gives it bacteria immediately |
| A hiding place | Lowers stress |
| Separate net and bucket | Stops cross-contamination |
Keep it bare so you can see waste and spot problems easily.
What to do during quarantine
- Watch daily for white spots, clamped fins, rubbing, weight loss or odd breathing.
- Feed lightly and keep water clean with small changes.
- Treat only if you see a clear problem, following the medicine label.
- Wait several weeks without signs of illness before moving fish over.
The CDC recommends washing hands after working in any aquarium. Between tanks, it also stops you moving germs from the new fish to the old ones.
The white-spot disease guide covers one concern that can appear after a new arrival. The fish veterinary visit guide addresses obtaining professional assessment when observation raises a problem.
Questions people ask
Do I really need a quarantine tank?
It is the most reliable way to keep disease out of an established tank. Many outbreaks start with a new fish.
How long should I quarantine new fish?
Several weeks is common, long enough for hidden infections to show. Longer is safer.
Can I quarantine fish in a bucket?
Short term, a large heated container with filtration can work, but a small tank is easier to keep stable.
Should I quarantine plants too?
Plants can carry snails and pests. Rinse and inspect them, or hold them separately before adding them.
Where these figures come from
- Ichthyophthirius multifiliis (White Spot) Infections in Fish University of Florida IFAS Extension · edis.ifas.ufl.edu
- Fish, Healthy Pets Healthy People Centers for Disease Control and Prevention · cdc.gov
Figures last checked September 2026.
