I am currently using the 502 on a small tank at home
my only gripe is that if the filter pad gets clogged then the water will overflow all over the place.
To stop this from happening I have not pushed the filter pad all the way down by leaving a small gap at the bottom so that it won't overflow.
If the filter pad was slightly shorter would of been good.. which means that if the pad did clog up it would flow over the filter pad and into the tank.. not out the back over the filter and then onto the floor.