My metal racks are from a local commercial shelving company, they are in branded so I don’t know who makes them. They are a rivet type shelving and are adjustable about every inch. They do have heavy duty cross bars that have no deflection under the weight load of the tanks. I also add 3/4” plywood shelves on each level.
Of note; these aren’t sold in a kit each piece is individual, do for a unit I buy the uprights I need, the side to side rails in the load bearing weight category I want (there are three types), and the side a middle supports in the depth I want. I buy and cut my own plywood as having them do it is too expensive. I also do use a metal strap to my walls somewhere near the tops of the units.