Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Nitrifying bacteria are not fast growing species.
If they are constantly being removed from one area (filter media) then the best population will be elsewhere in the tank. On the substrate, on plant leaves and stems, on driftwood...
Then you introduce new filter media and the bacteria start growing on it. But all the established bacteria are taking a lot of the ammonia, so there is not a lot available to the bacteria trying to get going on the new filter media. So growth is slow. Then that media is thrown away, and the bacteria in the rest of the tank remains to take care of the ammonia.
Throwing away the filter media, or cleaning it with chlorinated water often enough to keep the bacteria population very low is not going to cause a significant cycle in the tank as long as there is other media (substrate etc.) for bacteria.
Note R.sok's post, #12. A bare bottom tank has more bacteria in the filter, so the loss is significant.
Plants are also a part of the bio filter, and they also help pick up the slack when small amounts of bacteria are removed.