Ever try picking up a five gallon container of drinking water? It's heavy! The equivalent gallonage of aquariums is even heavier, considering the tank itself, aquarium gravel, ornaments... Such gear needs to be set upon a surface that is very sturdy... and more. Aquarium stands need to be level and planar... that is, it's important that the tank itself and water in them be set upon something strong that supports the tank completely along its edge/bottom to prevent torsion of its seals, and possible catastrophic breakage.

    Such structures are available as commercial aquarium stands, as well as DIY projects for those inclined. Some folks have counters and free-standing furniture that can work as well, with an eye on the inevitability of water spills and consequent possible damage from same.

    Another important consideration in choosing an under-support for an aquarium is the floor underneath it in turn. Fully set-up freshwater systems weigh about ten pounds per gallon... along with the weight of the stand, it's important to make sure the floor/foundation can support the total weight... evenly. You may be fortunate and get by w/o doing anything to your floor support, or possibly luck out by "spreading the weight" of all by providing continuous support (as opposed to legs) under the stand/support, but it's a good idea to "practice fill" an empty tank on its stand to make sure the floor is strong, and the whole construct level and planar/flat.