I was recently in the fish lab at the Toronto Zoo, and they us ACs on all their saltwater tanks. "Overfiltering" is a term I hate, as it is misleading, in the way it is used. If you mean having more fish because you have more filtration, it is only partly true. It doesn't matter how many filters you put on a tank, more fish means more water changes, of larger size. While I can't speak to the salt water side of the hobby, filtration in general, produces nitrates, as the final product. Once you have adequate filtration, that reduces ammonia and nitrite to 0, adding more filtration will not improve the situation; you will still have the same amount of nitrate produced, regardless. The argument goes, that more filtration will keep a tank visibly cleaner, but, this again is misleading, as whatever, was in the tank, that is now unseen, is in the filter, so is still part of the tank.
In a nutshell, more filtration will not preclude cleaning the filters less often, or changing less water. That is the fallacy of "overfiltration".
