I've seen several tanks where the bottom is plywood but with glass sides.
I also got pretty far along in making a triangular plywood tank for the corner of my living room. But without 90 degree angles the screws had much less wood to dig into to connect the corners. I eventually scrapped the idea for concerns on structural integrity. My humble recommendation would be to purchase a kreg jigg specialized to set screws in non-90 degree joints.
Yeah I was planning on using my pocket hole jig and running a spine down the angles for a little more grab. Really though I'm fiberglassing everything so that will be the main structural component. I'd absolutely love to do it so that the glass is uninterrupted like in that video but I don't have the guts to attempt to join mitered glass or acrylic.
Due to space constraints, The only way I can adequately house my rays and arowana is in a 5 sided tank. There is a doorway right in my way. Is this doable? Any thoughts or opinions? Would love to hear what you guys think.