Quarantine, Isolation or Hospital Tanks

Author: Last updated:

Fish behind quarantine tape

We are often told that we should quarantine our fish before introducing them, but few fish keepers actually do, with cost and space being the main concerns. A separate tank can be used for a number of purposes however, and is a very useful tool if you keep rare or delicate species, have health problems, or fish which unexpectedly breed.

Uses for an isolation tank

Because of the wide range of uses a separate tank can have, it may be best referred to as an 'isolation' tank rather than a quarantine tank. Quarantining is however, one of the biggest uses and if you have a large variety of high-value or prized livestock, then the last thing you need is for new fish to enter the aquarium along with a disease which could wipe out your existing stock. Using an isolation tank for a few weeks, or even a month, will allow you to observe new fish for health issues before they are introduced to the main tank, as well as allowing plenty of time for the new fish to become acclimated to your water conditions.

An isolation tank also comes in very handy if diseases occur in an established system. Treating for health problems can be quite a stressful experience for fish, and with many treatments based on strong chemicals there are often non-desirable side effects. Removing affected fish from the main tank can dramatically help prevent the spread of disease and allows a milder preventative treatment to be used in the main tank while the affected fish can get a full strength treatment in isolation.

There are other reasons why fish might benefit from a spell of isolation, including being able to spawn and raise young in peace, recovering from bullying stress or even isolating a bully fish so that when returned to the aquarium its territory is no longer established.

The problem with quarantine tanks

If the use of our isolation tank is to get a fish from a stressed and weak state to a happy, healthy state, then it must provide the best possible conditions. This is where most 'quarantine' tanks become their own downfall. The traditional image, seen in many books and articles, is of a small bare glass tank with a few ornaments. This is not a great visual environment for fish, and for many species, will actually be very stressful. An isolation tank should have a dark substrate and plenty of natural hiding spots, including plants, giving a varied and natural environment for the fish. Whilst a bare tank can be argued to be more practical in terms of maintenance and observation, it may be the final straw in terms of the fish's health.

Keep it simple

All the equipment you need for an isolation tank is a hood, heater and filter - lights are not required and the fish will usually do better when bright light is avoided. A hood is quite important since stressed fish are more likely to attempt an escape by jumping, however both the tank and hood do not need to be stylish so the cheapest and simplest is usually fine. Filtration can also be kept minimal since there are only going to be a few fish at any time, a small power filter is fine, or if you are using the tank for raising fry a less powerful air-driven filter is best. The tank should be situated in a quiet location away from noise or visual disturbances, and depending on the location and the size of fish likely to be in it, as large as practically possible.

Setting up the hospital fish tank

Running an isolation tank continually has little benefit and with a few provisions, the tank can be left dry until it is required. To avoid the problem of having no useful bacteria in a new tank, the filter for the isolation tank should be used in the main tank until required. This will serve the purpose of creating a matured filter ready for use, and it can also be useful in the main tank as additional filtration and flow. When the isolation tank is needed, it should be filled with water from the main tank so that any fish are not transferred into completely different conditions and new fish can be acclimated to the same conditions. The heater should be set at the same temperature as the main tank, and the extra filter can be simply swapped from one tank to the other. Using this method you can set up the isolation tank ready for fish in just a few minutes. The isolation tank should contain hiding spots and plenty of live plants. Since we are not aiming to keep the plants alive they can literally just be thrown in and replaced if they begin to die.

Running an isolation fish tank

Fish will need to be kept in the isolation tank for varying lengths of time depending on why they are there, for diseased fish from the main tank you will need to wait until a few weeks after the fish have recovered before re-introduction. Quarantining can be about the same length, and only raising fry will be a longer-term situation. Maintenance should be similar to a normal regime, but because the tanks filtration may not be perfect, it is best to carry out increased water changes of up to 30% several times a week. Using water from the main tank to top-up with, rather than new water, will keep conditions the same as the main tank. Algae does not need to be cleaned from the glass, and although unsightly, fish will actually prefer mucky glass as it will provide a source of food and reduce the effect of external visual movements. Water quality is of vital importance so carry out regular testing and if you are using treatments, keep oxygenation as high as possible by using an air pump or situating the filter near the waters surface. Finally, feeding should be regular but controlled, since overfeeding will overwhelm the smaller filter and excess food can aid the spread of some diseases. For a good health boost or recovery, fish should be fed several times a day, but with very small amounts of good quality food. Using activated carbon or other chemical filtration medias will help to remove any excess pollutants that the filter may not cope with.

An isolation tank can be well worth the cost if it helps to prevent fish losses, and also provides a useful backup for heating and filtration in the event of equipment failure in the main tank. Whether it is used for treating ill fish, quarantining new fish, isolating bully fish, spawning or raising fry, it is a lot easier if you are prepared in advance.

Click to read the Latest Tropical Fish discussions from Thinkfish users.

Think Fish Tropical Fish Forum
Tropical Fish Market Place
Fish of the month

Helping Fishkeepers With Their Fishkeeping Needs Since 2006