you just dont want to place the maximum rating on it at all times, because then you have no margin for error, if you're not approaching that limit, at the very least mount it to a stuf on the wall to it wont sway or anything, but even then, i'd beef it up more. You could also use cinder blocks and plywood, have you considered this?
well I've had people recommend these because its worked for there tanks. I believe each shelf holds up to 1000lbs...I will only be keeping 20longs, 30longs, and 40breeders on it. Each of which is below the 1000lb mark with water in it.
I looked at the product description. It may be a steel frame, but it lists the shelves as particle board. Particle board loses structural integrity if/when it gets wet. If the shelves were metal, I would call this a good find.
Just my two cents also. I notice the 4 legs are all basically angle iron. What kind of flooring are you putting this on? I don't do the mathmatics all that well but it seems there would be quite a bit of pressure on those legs and the small footprint on the floor. 3-4 (depending on size) tanks = 600 lbs+ ?