I have an Aquaclear 802 and have never had a problem with my fish even almost getting sucked in. It IS a 5-6" fish so yeah, take that into consideration. If you have small fish, then you will want a prefilter. I also have my powerhead sitting about 4" from the bottom and i have sand. I have no problems with sand getting sucked up either, so you can kind of see that suction isnt really a problem in my case.RhomZilla said:You never mentioned what your planning to attatch to the other end... the intake part. You can just submerge your powerhead in the tank, no problem, but you'll need a prefilter on the other end (butt part) so that your fish doesnt get sucked up. And damn.. does an 802 suck!!!