Originally Posted by gopeder111
says I can problably keep the regal tang for a yr. or more before maybe out growing the tank because most of them I've seen take a long time to grow
This is a very bad idea and a bad fishkeeping practice. Buy fish suited to your tank. Fish shouldn't be thought of as a piece of rented furniture that can be returned when your done with it. It's stressful on the fish and unfair. Like mentioned already, this fish regardless of how small it is, needs more swimming room than a 20g will offer. And to keep one in a 20g for a year? That's just insane thinking.
Originally Posted by goperder111
If this doesn't work out I'm just going to get dwarf angelfish
A 20g is to small for a dwarf angel as well. They need no less than 30g. Small tanks can be very limiting but you still have a good many options for some very colorful fish. Fish suitable to a 20g would be things like damsels, clowns, basslets, gobies, some types of blennies, dartfish/firefish and probably others that I just can't think of right now. There is also a variety of ornamental inverts that would add a splash of color and movement to the tank as well as perform clean up duties. Here is a link to liveaquaria. They have a section for fish suitable to a nano (anything under 30g) type tank. Maybe this will give you some ideas.