I have a 7-8'' redtail payara ( vampire tetra) in a 230 with a 21'' Black aro and 6'' atf, 5 clown loaches,2 7'' bala sharks, one 7'' male Frontosa and 1 synodontis cat and 1 5'' male motoro ray and all is going very well. I keep my fish well fed at all times though. I must agree, the vampire tetra is spectacular to watch hunt and feed. Already at 7-8'', I can see it's teeth 6 feet away from the aquarium. They are really white. They also shed their teeth like a shark and have replacements folded down ready to pop-up into place within 2-3 days. I've also noticed the fish will not feed during this time. I have also noticed that the redtails seem to be quite a bit more agressive and will stand their ground against pretty much anything, at least mine does. I can't wait till it's 12'' or more.
Mike