Well, it's actually a 12gal. I'm hoping to get a 30 so he can have a partner and more plants. As far as the red tails go, I did have three as recommended, but one had died. He was a little lean when we got him and I was hoping he'd grow out okay. I was wrong. These two have been cruising together and no aggression towards each other. I'm still lookin' at getting a 3rd though.