It’s true a 5” or 6” wall aquarium can hold most pet fish species however, a bigger aquarium can hold more. You can put a deeper aquarium in your wall by having one or both sides overhanging. This can be done by having a base underneath 1 ½” thick and firmly secured to the wall studs below. You will not need any additional supports as long as your overhang on one side doesn’t exceed 2”. If you want one side to hang out more you will need to add some triangular/gusset pieces to support the base.