Every experienced reef keeper has heard the same advice: quarantine everything. It’s tempting to skip it when you bring home a beautiful new fish. But one sick fish can introduce parasites that wipe out an entire display tank. Here’s why you should quarantine new saltwater fish and how to set up a simple quarantine tank.
Quick Answer: Quarantine new fish in a separate tank for at least 2 to 4 weeks, and many hobbyists prefer 4 to 6 weeks. This lets you watch for disease, treat problems without harming your display tank and help fish recover from shipping stress. A basic quarantine tank needs a heater, filter, hiding spots and test kits.
Why Quarantine Matters
Wild-caught and even captive-bred fish can carry diseases without showing symptoms right away. Common problems include:
- Marine ich (Cryptocaryon irritans)
- Marine velvet (Amyloodinium)
- Brooklynella and Uronema (protozoan infections)
- Flukes
- Internal parasites
- Bacterial infections
Once a parasite like ich or velvet is in your display tank, getting rid of it usually means removing every fish for weeks. The Merck Veterinary Manual recommends quarantining new fish to reduce disease introduction.
What You’ll Need
| Item | Notes |
|---|---|
| Tank | 10–40 gallons, depending on fish size |
| Filter | Sponge filter (ideally pre-seeded in your sump or display) |
| Heater | Keeps temperature stable |
| Hiding spots | PVC pipe sections work well and are easy to clean |
| Lid | Prevents jumping |
| Light | Simple, low-intensity |
| Test kits | Ammonia, nitrite, salinity, pH; copper kit if using copper |
| Separate tools | Net, siphon, bucket used only for quarantine |
Avoid sand and live rock in quarantine. They make cleaning harder and can absorb medications like copper.
How to Set Up a Quarantine Tank
- Fill with water from your display tank or freshly mixed saltwater.
- Add a cycled sponge filter that has been living in your sump or display.
- Set the heater to match your display.
- Add PVC hides.
- Test ammonia and nitrite daily while fish are in quarantine.
Quarantine Approaches
| Method | What it involves |
|---|---|
| Observation | Watch fish for 4–6 weeks; treat only if signs appear |
| Prophylactic treatment | Treat all new fish with proven protocols (such as copper or medications) whether or not signs appear |
| Tank transfer method | Move fish to clean tanks every 3 days to break parasite cycles |
Many hobbyists use prophylactic treatment for common parasites, especially for fish prone to ich and velvet. Ask an aquatic vet or experienced fish store which method suits each species.
Daily Quarantine Routine
- Watch breathing rate, appetite and behavior.
- Look for spots, dust, cloudy eyes or frayed fins.
- Feed varied, nutritious foods. See what to feed saltwater fish.
- Do small water changes as needed to keep ammonia at 0.
- Keep the lights dim and the area calm.
Moving Fish to the Display
When quarantine is complete and the fish is eating well with no signs of disease:
- Match temperature and salinity between tanks.
- Move the fish with a net or cup.
- Turn display lights off for a few hours to reduce stress.
- Watch for aggression from existing fish.
Quarantine Inverts and Corals, Too
Corals, snails and crabs can carry parasite stages in their water. Many reef keepers hold them in a fishless tank for several weeks or dip corals before adding them.
Common Quarantine Mistakes
- Using an uncycled tank, causing ammonia spikes
- Ending quarantine too early
- Sharing nets or equipment with the display
- Using copper in a tank with invertebrates
- Overcrowding the quarantine tank
When to Get Help
Contact an aquatic vet if:
- A fish stops eating for several days
- You see white spots, dust or rapid breathing
- Multiple fish get sick
Frequently Asked Questions
Can I skip quarantine if the store quarantines fish?
Some stores do excellent quarantine. Others hold fish only briefly. Ask what they do, but many hobbyists still quarantine at home.
How big should a quarantine tank be?
Big enough for the fish to swim comfortably. A 20-gallon tank works for most small fish.
Do captive-bred fish need quarantine?
Yes. They’re often healthier, but they can still carry disease from shared systems.
What do I do with the quarantine tank between fish?
Keep the sponge filter in your sump so it stays seeded, and clean and dry the quarantine tank between uses.
Should I quarantine fish from a friend’s tank?
Yes. Fish from home aquariums can carry parasites too, even if the tank looks healthy.
Can quarantine stress fish?
A calm, clean quarantine tank with hiding spots usually reduces stress compared with being chased by established fish in a display.
This article is for general information only and isn’t a substitute for professional veterinary advice. If you’re worried about your pet’s health, contact your veterinarian or an emergency animal hospital.
