Before introducing a new fish to an established tank, a period of quarantine is recommended. A 10-gallon aquarium equipped with an inexpensive box or sponge filter powered by an air pump is all that's needed for most quarantine setups. A small heater and aquarium hood may also be helpful. You should keep a logbook and record dates, behavior, feeding and general appearance as they apply to your new fish. Once fish have been introduced to a quarantine tank, no new fish should be added until the quarantine period is complete.
For more information, please read How To Quarantine Your Fish