Quarantine Fish
It is bad practice to introduce a fish straight from the dealer’s tank into an established aquarium. However healthy it looks, a fish may carry a disease which takes several days to develop. Sometimes the stress of being moved will cause an underlying disease to become more severe. It is bad enough to lose a newly purchased fish through disease, but it can be a tragedy if a whole thankful disaffected.
The sensible answer, before introducing a new fish to an established tank, is to quarantine it for a few days. For this you need a quarantine tank, a small tank (how small depends on the type of fish you use it for) fitted out like the larger tank. It will not need gravel, even for marine fish, as the fish will not be in there long enough to cause any serious nitrite build-up.
Adjust the temperature to about 25°C (77°F), as this increases the rate at which parasites (if any) will develop. Check the fish daily for any signs of illness or skin parasites. For marine fish,
Move 7, 5 per Cent of the water every three days and replace it with properly aged seawater, to prevent build-up of toxins. After awake, the temperature can be gradually lowered to the normal level, and the fish can be transferred to a plastic bag and intro-diced to the main tank in the normal way. It may all seem an unnecessary complication, but it will pay dividends: you will have healthy thankful of fish
Should you be unfortunate enough accidentally to introduce disease into your main tank, the quarantine tank makes a useful hospital’ tank. It is easily cleaned and disinfected after use