In an enclosed ecosystem such as an aquarium, disease does not just occur spontaneously from no-where. It is always induced either by an external source such as live foods or a result of an environmental factor such as poor tank conditions.

After spending time to achieve good water conditions and establish a healthy aquarium it is a wise precaution to quarantine new additions such as fish and plants to prevent the introduction of a disease to the aquarium.

A smaller aquarium can be set aside as a quarantine tank and arguably will pay for itself the first time it is used. This aquarium need not be anything special. A small 2 gallon plastic tank fitted with a 50 Watt heater and an air driven sponge filter is the minimum that is required. This aquarium can be furnished with or without a substrate but do provide some rocks or an upturned terra-cotta flower pot in which fish can shelter. The addition of some plastic plants helps afford some security so that any new fish do not feel too exposed.

Plastic plants in this aquarium are ideal as you may need to medicate this aquarium frequently. Often chemical medications for fish have a detrimental effect on real plants.

If you do not wish to permanently set up a dedicated quarantine aquarium, you could run a sponge filter in the main aquarium and transfer it, and some old tank water to the quarantine tank when required. I have a dedicated quarantine aquarium that also doubles as an occasional breeding aquarium. I keep it very lightly stocked with just a few fish to keep it ticking over ready for any new additions. Usually I keep guppies here and use the fry as a source of live food.

New fish should be quarantined for a minimum of four weeks but better six weeks. During this time one should observe the fish closely. Ensure that the fish are feeding, look for any signs of disease and administer the appropriate treatment. I like to allow a period of six weeks after any signs of disease before finally transferring the fish to the main aquarium. Only after this time can one be certain that no infection is being introduced.

This is also a good period enable the fish to adjust to its new water. If your tap water differs substantially to that of your fish store, use this time to slowly adjust the pH or hardness etc.

Maintaining a small quarantine tank also helps to guard against introducing too many fish to the show aquarium at one time. Invariably, the quarantine tank will only be able to cope with a few new additions without overloading the filter and this threshold will be less than the main tank. I tend only to purchase about four to six fish in any one quarantine period to prevent over loading the filters. For this reason, shoals should be built up over a period of months. This has the added advantage that should you be able to maintain a fish for its lifetime the entire shoal won't die at the same time.

Personally, I tend not to quarantine plants as the parasites that infest plants tend not to attack fish. However, to restrict an outbreak of snails or to protect some established plant species in the main tank, one can quarantine plants for around 3-4 days.

One final note. Resist all temptation to fully stock a quarantine tank. Doing so means that you will need an other quarantine tank as the current one is full. The purchase of a subsequent quarantine tank often results in the original quarantine tank becoming a display aquarium and this cycle rapidly continues. Aquarists may not mind "just one extra aquarium" but partners are often less understanding!