It does multiply however the reason why you need to retain the BB as much as possible is that the diminishing colonies cannot do its job in containing ammonia and nitrite in the shortest time possible. Once both substances elevate dangerously, your fish are at a risk being intoxicated in the process.
No, you don't keep the filter as often as you think is necessary. Clean only if it really needs it.
No, you don't keep the filter as often as you think is necessary. Clean only if it really needs it.