Agreed, but use 3/4", much more substantialIf it were mine... I'd use 1/2"plywood sheet with a foam insulation sheet on top, but also add four 2"x4"legs under the 2 center supports. Glass tanks have the weight on the perimeter, acrylic is the entire bottom.
Sorry, didn't mean to suggest legs in center of supports...meant on sides next to 'uprights' that are already thereInstead of adding legs down the stand in center of supports, add 2x8 on end from front to back under supports. So you don't kill all the space in stand