No, no, no - to "I'll see what I can find at the petstore" - you know that doesn't work for you. You see something so cute you can't resist, bring it home, and everyone is yelling at you. Your 20 gallon tank is a given - you can't change that, so if it is too small for another cichlid, you have to look at some other possibilities. You have had so much fun stocking, why not just take your time - once you are done, you are done. Spread the fun out a bit.