How to Quarantine Sick Fish

Why Quarantining Sick Fish Is Essential

When a fish shows signs of illness, isolating it immediately is one of the most important steps you can take. Quarantine protects healthy tankmates from contagious diseases, allows you to treat the sick fish with targeted medication without affecting the entire tank, and reduces stress on the sick fish by removing it from competition and aggression.

When to Quarantine a Fish

• Any fish showing signs of ich, fin rot, dropsy, or other visible disease
• New fish before introducing them to an established tank (preventive quarantine)
• Fish being bullied or injured by tankmates
• Fish recovering from treatment that needs monitoring
• Any fish behaving abnormally — hiding, not eating, gasping

What You Need for a Quarantine Tank

• A separate tank (5–10 gallons is sufficient for most fish)
• A simple sponge filter or air-driven filter
• A heater
• A hiding spot (a piece of PVC pipe or decoration)
• Water conditioner
• Medication appropriate for the illness

If you don't have a separate quarantine tank, the Fluval Multi-Chamber Breeding Box can serve as a temporary isolation solution within the main tank. It separates the sick fish while keeping it in the same water, which reduces the stress of a full tank transfer for mildly ill fish.

How to Set Up a Quarantine Tank

1. Fill with water from the main tank — this ensures the sick fish isn't stressed by a sudden change in water chemistry. Top up with fresh treated water if needed.
2. Install a heater and filter — keep temperature consistent with the main tank.
3. Add a hiding spot — a stressed, sick fish needs somewhere to feel secure.
4. Test the water with the Varify 17-in-1 Water Test Kit before adding the fish.
5. Transfer the sick fish gently using a net. Minimize air exposure.

How to Care for a Fish in Quarantine

• Do 25% water changes daily to maintain excellent water quality
• Treat with appropriate medication — the MICROBE-LIFT Artemiss is a broad-spectrum treatment safe for freshwater and saltwater fish
• Remove carbon from the filter during medication treatment
• Feed lightly — sick fish often have reduced appetite
• Monitor closely for improvement or deterioration
• Keep the quarantine tank in a quiet, low-traffic area to minimize stress

How Long to Keep Fish in Quarantine

• Sick fish: Until fully recovered plus 7 additional days with no symptoms
• New fish (preventive): Minimum 2–4 weeks
• After ich treatment: Until no spots visible for at least 7 days at treatment temperature

Cleaning the Quarantine Tank After Use

After quarantine, thoroughly clean and disinfect the tank, filter, and all equipment before storing or reusing. Rinse with a diluted bleach solution (1 part bleach to 9 parts water), then rinse thoroughly with plain water and allow to dry completely before reuse.

Final Thoughts

A quarantine tank is one of the most valuable tools in a fishkeeper's arsenal. Even a simple 5-gallon setup can save lives by containing disease, enabling targeted treatment, and giving sick fish the calm environment they need to recover.