This is a cut and paste from the website:
The entire bottom of the aquarium must be fully and evenly supported on a flat, level surface at all times. The use of a perimeter support stand, as often used for glass tanks, will void the warranty. An appropriate stand for acrylic tanks will be strong enough to hold the weight, will have a top that is flat enough so that if the tank were set directly on it, there would be no dips or humps that would cause the tank bottom to not make contact with the top of the stand at any point before it is filled. For all practical purposes, the top of the stand must be as strong at any given point in the middle as it is on the perimeter. This means that a sheet of plywood cannot simply be set on top of a perimeter stand, as when filled with water the tank bottom could bulge down in the middle and put extra stress on the bonds. There must be cross braces on the top of any stand before the flat stock is added, regardless if it is wood or steel. The top of the stand must have at a minimum one layer of ¾” flat stock, usually plywood. 2 layers are recommended with the top layer unattached so that shims can be driven between the 2 sheets to tighten up any voids if necessary. A layer of extruded polystyrene foam is also recommended between the stand top and the aquarium, to compensate for small imperfections in the top of the stand.