Originally Posted by binka_nugget
Torn fins can be from biting.. which is usually because of stress. The filter might be stressing him out too much.
What size tank is he in? A filter isn't needed in anything smaller than 5 gallons.. I personally don't put a filter in unless it's 10 gallons or larger. Everything else gets 100% WCs. A filter is supposed to help sustain the "cycle" (ammonia gets eaten by nitrites which get eaten by nitrates). It's very hard to have a steady cycle in anything smaller than 10 gallons.