Quarantine Tank Size Calculator
Calculate the right quarantine tank size based on fish species, count, and quarantine duration for healthy fish.
A quarantine tank (QT) is a separate aquarium used to isolate new fish before introducing them to your main display tank. This practice prevents diseases like ich, velvet, and bacterial infections from wiping out an established community.
Quarantine Tank Sizing Formula
Minimum QT Volume (gallons) = (Number of Fish × Fish Adult Size Factor) + Base Volume
Where:
- Base Volume: 10 gallons minimum for any quarantine setup (enough for a heater, sponge filter, and hiding spots)
- Fish Adult Size Factor: gallons per fish based on adult body length
| Fish Adult Length | Gallons per Fish | Examples |
|---|---|---|
| Under 2" (small) | 1.5 gal | Neon tetras, endlers, ember tetras |
| 2–4" (medium) | 3 gal | Guppies, mollies, dwarf gouramis |
| 4–6" (large) | 5 gal | Angelfish, rainbowfish, larger barbs |
| 6–10" (XL) | 8 gal | Oscars, discus, large cichlids |
| 10"+ (jumbo) | 15 gal | Arowanas, large plecos, pacu |
Standard Quarantine Protocol
| Phase | Duration | Treatment |
|---|---|---|
| Observation | Days 1–7 | Watch for symptoms. Maintain pristine water quality. |
| Prophylactic treatment | Days 8–21 | General anti-parasitic (e.g., Praziquantel) and/or antibacterial |
| Final observation | Days 22–30 | Confirm no symptoms. Match QT water parameters to display tank. |
Total recommended quarantine: 4–6 weeks for freshwater, 6–8 weeks for saltwater (due to ich lifecycle at lower temperatures in marine systems).
Worked Example — Quarantining 6 Neon Tetras
Fish size: Under 2" (small). Gallons per fish: 1.5. Fish volume: 6 × 1.5 = 9 gallons. Base volume: 10 gallons. Recommended QT: max(10, 9 + 10) = 19 gallons → round to standard 20-gallon tank.
In practice, a 20-gallon long tank is ideal. The extra length gives small schooling fish room to swim, reduces stress, and provides stable water parameters.
Water Change Schedule During Quarantine
| Tank Size | Water Change Frequency | Volume per Change |
|---|---|---|
| 10 gallon | Every 2 days | 30% (3 gallons) |
| 20 gallon | Every 3 days | 25% (5 gallons) |
| 30+ gallon | Twice per week | 20% |
Essential QT Equipment
- Sponge filter (seeded from main tank for instant cycle)
- Adjustable heater
- Thermometer
- PVC pipe or terracotta pot for hiding
- Bare bottom (no substrate — easier to clean and observe)
- Lid/cover (stressed fish jump)