I have a 15g with 5 tiger barbs, one pleco and one shark catfish. I've noticed my fish always cluster on the right side of the tank...the barbs in the middle and the other two toward the bottom. The filter is on the left side of the tank and is one that sucks water from the near the bottom and pours it back in from the top (I don't know what that kind is called). It makes quite a current in the tank, even when I fill the tank pretty high so the water almost flows out of the filter rather than dropping. I'm wondering if the current is too strong for the fish and might tire them out. Then again maybe fish LIKE current. Anyone have any ideas? What kind of filter do I need if this one is wrong? It does an awesome job so I hate to change unless I need to--my last one was useless. Thanks!