It's unlikely he'll stop growing to be honest, and like Luke said, even if he does, it'll shorten his lifespan significantly (and if he doesn't he won't fit anyway). I know how hard it is, but he needs to have a HUGE tank. I can't see one smaller than 6 x 2 x 2 being suitable. Like I said, I know it's hard, we had to give up our chocolate albino liposarcus because he was sold to us as hypostomus punctatus by PAH. It's easy to tell if he's liposarcus pardalis (the giant ones) as he'll have roughly 11-14 dorsal rays. If he was a hypostomus, he'd have 5-8.