Quarantine for New Fish
New fish can carry diseases that never show in the store. A separate quarantine tank is the one habit that protects everything already living in your display tank.
Key facts
- Quarantine keeps new arrivals separate from an established tank long enough to catch a problem before it spreads.
- Recommended length varies by source, commonly 2 to 6 weeks; Aquarium Co-Op specifically recommends 4-6 weeks since the last symptom or death was seen.
- A bare-bottom tank is easier to keep clean and easier to spot a problem in.
Why bother
New fish can carry ich (Ichthyophthirius multifiliis), flukes or internal parasites that show no symptoms in a crowded store tank. Quarantine gives an observation window and lets you treat one tank if needed, instead of medicating the whole display tank, including fish that never needed it.
How long
Sources disagree on the exact length: some cite a 2-week minimum, others 30 days. Aquarium Co-Op specifically recommends 4-6 weeks, counted not from the day the fish arrived but from the last time a symptom or death was seen in the quarantine tank.
Setting up a quarantine tank
- Bare bottom, no substrate — easier to keep clean and easier to spot parasites or unusual waste (per Aquarium Co-Op).
- Gentle, low-flow filtration — a sponge filter is recommended, ideally already seeded with bacteria (see the choosing-a-filter guide).
- Hiding spots and decor — sick fish often want to hide, and shelter reduces stress.
- Water parameters and temperature reasonably close to the main tank — we couldn't find a specific cited tolerance, so this stays qualitative rather than a hard number.