power filter: See if you can reduce the water flow. If not then you have two options: You can either rig something up to slow down the flow or change the filter and replace it with one that has a flow regulator. Your fishstore should be able to help you select one. Trying to rig something up yourself may be a bit fishie (hehe pun untended) because if you do it wrong you can affect the efficiency of the filter in such a way that your water quality will degrade too much. Water can never be stopped. It should always flow, but sometimes by adding a piece of brand new sheer fabric (mesh like), adding some floss, and then tying the whole thing around the mouth of the intake tube, you can create a sort of 'diffuser' which will prevent the water from flowing in very freely, thus reducing the volume of water moved and reducing the suction effect. Do not use anything metal to tie the contraption. Only a plastic tie or a rubber band (get it from fishstore). You will need to remove it and rinse it once every two weeks or so, or anytime it starts looking dirty (it will fill with small particles over time). If you can spend the dough, getting another filter would be safer and better.

corner filter. This is a lot easier to fix: Just a get a valve, put it on your airline to restrict the amount of air flow coming from your airpump. And VOILA the trick is done.