Sigh, I inherited the danged thing along with a tiny albino cory and a tetra. When I got them they were in a plant vase without any sort of air flow or filtration. I wasn't just going to let them die in the vase so picked up a 2 gallon mini tank to keep them alive for a while. Then the original owner decided that he didn't want them back. Along with my missing water this is what
led to the 20 gallon cube.
I know that the pleco can easily outgrow the tank but already have plans for the possibility of at least a 50 gallon tank. May sound funny but I'd get 500 pounds of sand bags (or more if I went larger as to a tank) first and then bounce on them. I live in a third floor apartment and would want to proof that the floor would handle the ~500 pounds of a 50 gallon tank.
I have plenty of time to figure all this out as the danged pleco won't outgrow the 20 gallon tank for a while even though it eats like a pig.
LOL! Then I have to deal with my 'demon cockatiel' which is totally fascinated by the tank. Here is a pic that shows his interest when I first had the tiny tank.

He sat there for over an hour just watching.