It depends on what you mean by maintain. The amount of active bacteria and Archaea in a tank are determined by the ammonia levels being produced in the tank. As long as there is some level of ammonia and then sufficient oxygen, inorganic carbon and a bit of Iron, the bacteria will be active. If what they need become unavailable, then they are likely to go dormant.
If you had fish in the tank and now have only snails, then the odds are that the amount of bacteria will decline. Bear in mind that, if live plants are present, they use ammonium and what they use the bacteria cannot. However, no matter how many live plants are in a tank, there will still be some amount of the microorganisms present.
The problem with trying to hold a level of bacteria in a tank that the way to do it is to add ammonia. But when there are living things like inverts and/or fish present, we cannot do this.
