I got one of the 9500 because it was onsale, mistake of course. All it was powering was an 8" bubble wand, one air stone, and a bubble disk all in only 12" of water (ie, not deep at all). It worked fine at first, then a week or two later it started making this horrible loud rattleing sound. Took it apart and right next to where the 'pistons' are is a peg hole for a screw. If too much resistance (which wasn't even enough to power ANYTHING anymore) the pistons bang against the plastic peg. Having to buy a new air pump now, going with different brand.