Whilst there is often a lot of coverage about starting a brand new tank and adding your first fish there is far less about what you need to do to add more fish to an existing fish tank with a fish population. It is a misconception that simply adding further fish won't result in implications when, in fact, it can be just as difficult as starting a new tank from scratch. A stable (mature) existing aquarium is generally in balance with the number of fish it contains. The number of fish is supported by a population of beneficial bacteria which convert ammonia and nitrite through the nitrogen cycle to produce the less harmful end product called nitrate. The overall size of the bacteria colony in your existing tank is therefore representative and restricted in its size by the number of fish and the associated waste (ammonia) they produce. By adding, say one new fish, a very gradual increase in ammonia would be expected and the bacteria associated with the conversion of the increased ammonia and nitrite would increase in population size and begin to convert ammonia to a low level until the bacteria population size is once again in balance with the changed water parameters. This is also helped by not feeding the fish for a day or two to avoid the further introduction on additional ammonia. Beyond this, feeding the fish very lightly for a number of further days would gradually increase the water ammonia and allow the bacteria colony to continue to grow. This process can be monitored with the aid of a water test kit. However, get this wrong, particularly through adding too many new fish (i.e. bio-load) in one go and then also feeding them would very likely result in a fast spike in water ammonia levels that could be detrimental to all the aquarium's fish. In this situation, the time it would take for the beneficial bacteria colony to expand in size may not be fast enough to keep on top of and deal with the toxic build-up of ammonia. The ammonia would raise and may continue to increase to reach a level that could cause harm and/or death of aquarium fish (in a scenario called "new tank syndrome"). One way to avoid this situation is to dose your aquarium with additional bacteria. This additional bacteria would help to cycle your aquarium (convert ammonia and nitrate) in a process that can be safely completed in a matter of days, rather than weeks and months. There may be a good number of reasons why you may want to add more fish to an existing aquarium. This video does exactly that. It steps you through the process for doing this and, if done correctly, will help limit the issues that could otherwise lead to disastrous consequences for both existing and new fish.

• published: 10 Mar 2021
• views: 319