When most people start taking care, they often start off with small tanks. After time and experience, a lot of hobbyist want to upgrade their tank to a larger size. When doing this there is one big issue that you can run into, re-cycling the tank. When a new tank is being set up, the tank goes through the nitrogen cycle. This is the process where ammonia is broken down and eventually beneficial bacteria is produced. The beneficial bacteria is what removes the dangerous ammonia and nitrite that will harm fish. This is something that a lot of people don’t think about when they get a new tank that they want to transfer everybody into.
Re-cycling the tank will only be an issue when a new filter is used for the new tank. If the same filter is being used for the new tank, then it shouldn’t be an issue. However, most bigger tanks will require getting a new filter. If everything is transferred to the new tank, including the fish it would cause the tank to re-cycle. That will cause a dangerous level of ammonia and nitrate to be introduced into the tank, probably killing a lot of the fish. There are a few ways to introduce a new filter.
One safe way of doing this is to cycle the filter in the existing tank. If you hook up both filters to the old tank, it will give the new filter a chance to build up the beneficial bacteria. This should be done for at least 2 weeks before setting up the new tank. If you are still skeptical, the next safest step would be to set up the new tank, but this time have both of the filters on the new tank. This can be done for another 2 weeks, and then it would be safe to take out the old filter and run just on the new filter.
Another safe way to upgrade tanks, is to set up the new tank and re-cycle it safely. This would entail either having only a few fish for a few weeks, monitoring the water parameters until it becomes safe. This is a safe method, however it requires being able to have both tanks up and running at the same time for a few weeks. Having two tanks running takes up a lot of space, and not everybody has room for both of them.
For either of these methods, there is one way that can help speed up the process. It involves taking some filter media from the old filter, and squeezing it out into the new tank or filter. This will cause the water to become dirty and cloudy for a day or two, but it also gives the new filter a lot of beneficial bacteria that has already grown in the old filter. Be aware though, if the bacteria is introduced, and it does not have any food (ammonia) then it will all die. So make sure you do not do this until you are sure there is a food source for the bacteria.