I picked up a freebie 18" cube several weeks ago that ultimately I'd like to use as an aquarium. I've filled it with water, and it didn't leak, but I only did it as a test to make sure the edges were water tight. In the long run, I have no idea if it would hold up. Maybe you can help me. It's, I think, acrylic (though quite possibly plexi glass) and roughly 5mm (just shy of a 1/4 of an inch) thick. Think it could stand up to the pressure?