some of those casters can support tons litteraly. but then you start getting into lb/sq inch problem with your flooring. your surface area is going to be reduced to probably no more than 4 square inches of floor space. may not be good for the floor. that is a lot of weight. think of it like this...55 gal = ~700lbs maybe depending on rock. divided by 4 wheels im guessing 160 lbs for one sq inch on the floor. that is the equivelent of an average mans body weight in jsut a sq inch on the floor. that is a lot of pressure. i dont think the stand could take it unless is is reenforced with steel in the frame. wood would just rip at the fibers and like was mentioned if one wheel broke the whole thing is comming down more than likely.