Sam here. Quarantine tanks are very important for new or sick fish. When bringing fish home they should be housed in a quarantine tank for the first couple of weeks to be sure they are in good health. There are several reasons for this.
Just like people, fish get stressed out when they are suddenly thrust into a new environment, and this stress only increases in the presence of other fish. A quarantine tank allows your fish to “come down” from that intial home stress, making it healthier to cope with life in the main aquarium.
2. Easier and Cheaper to Medicate
Transporting or moving fish is a stressful time, and often leads to disease. Fish commonly contract bacterial infections, fungal infections or parasitic infections after coming home, and the last thing you would want would be to spread these to your other fish. In addition, an isolated sick fish is much more ecomomical, quicker and easier to medicate than one in a large display tank. Many common fish medications, such as copper or formalin based, are detrimental to other tank inhabitants as well as biological filtration, so keeping an isolated quarantine tank is essential.
3. Easier to Observe
There is no better way to ascertain the health of a fish than simply by watching it. Large display tanks can have lots of nooks and crannies for fish, especially stressed ones, to hide. Having an isolated quarantine tank makes it quick and simple to gauge when your fish is in prime shape.
Have a great New Year,