Use a separate heated and filtered tank or food-safe tub sized for temporary holding. Give fish shelter, stable temperature, conditioned water and adequate oxygen. Use dedicated nets and siphons, observe daily for abnormal breathing, appetite, spots, sores or fin damage, and avoid sharing water or wet equipment with the display tank. Quarantine duration varies by risk and protocol; many hobbyists use several weeks rather than a few days.
Quarantine is less glamorous than aquascaping, but it is one of the few tools that can stop a single new purchase from exposing an entire established population to disease. It also gives you a smaller, simpler system in which to monitor feeding and behaviour closely.
What a quarantine tank needs
| Item | Purpose |
|---|---|
| Separate tank or clear tub | Physical isolation |
| Mature sponge/filter media | Biological filtration with gentle flow |
| Heater where required | Stable species-appropriate temperature |
| Thermometer | Independent temperature check |
| Lid | Prevents jumping and reduces disturbance |
| Simple hides | Security without complex decor |
| Dedicated net and siphon | Reduces cross-contamination |
Keep the setup simple
A quarantine tank does not need display-tank decoration. Bare bottom makes waste easy to see and remove; inert hides such as smooth PVC sections or easy-clean ornaments provide cover without making inspection difficult.
Avoid sharing nets, siphons, filter sponges or wet hands between quarantine and display tanks without appropriate cleaning and drying.
Daily observation matters more than gadgets
Record anything suspicious with the date. A pattern over several days is more useful than trying to remember whether a mark looked different yesterday.
- Is the fish eating normally?
- Is breathing unusually rapid or laboured?
- Are fins clamped, frayed or held normally?
- Are there spots, ulcers, swelling or excess mucus?
- Is swimming balanced and coordinated?
- Is waste appearance markedly abnormal?
How long should quarantine last?
There is no universal number that covers every pathogen, species and source. Aquarium Co-Op recommends a multi-week period and describes 4-6 weeks as a cautious hobbyist approach in its protocol.
A very short quarantine can still miss diseases with delayed signs. The more valuable or vulnerable the established population, the stronger the case for a conservative observation period.
Medication is not automatically required
Some hobbyist quarantine protocols medicate preventively; others observe and treat only when signs appear. Medication choice depends on diagnosis, species tolerance, local availability and product instructions.
Do not mix treatments casually or dose from memory. If treatment is necessary, calculate the actual water volume and follow the medicine label precisely.
Moving fish from quarantine to the display
Only transfer fish that are feeding, behaving normally and show no active signs of disease under the protocol you chose. Match temperature and water conditions, then use clean transfer equipment.
Do not move quarantine water into the display tank.
Related aquarium tools and guides
Frequently asked questions
Do I need to quarantine every new fish?
Quarantine is especially valuable when adding fish to an established tank because it reduces the chance of introducing disease. The level of caution you choose depends on the source, existing livestock and your risk tolerance.
Can I use a plastic tub as a quarantine tank?
Yes, a suitable food-safe clear tub can work if it is stable, heated where necessary, filtered or otherwise safely managed, covered against jumping and large enough for the temporary fish.
Should I keep a quarantine tank running all the time?
Not necessarily. Many keepers keep a spare sponge filter seeded in an established aquarium so a quarantine tank can be assembled quickly when needed.
Sources and further reading
This guide separates general aquarium arithmetic from fish-welfare decisions. For species-specific limits, always check the needs of the fish you intend to keep.