Tricky one really... Easy decision when it comes to rehoming,(you definately should) but some people refuse to see something right in front of their nose. No offense meant by that, but its sometimes the case. Most red tails will be pretty peaceful for a long time, its with age that the territorial aggression develops. Sometimes it can even happen overnight.
The ball is in your court really, it'd be wise to only have fish in there that are suitable to the tank specs and the community you intend to keep. I would certainly like to think that most people on here would agree, but its more of a case of opinion in your particular case.
Red tails go best with larger fish really.(not a chance in that tank) So get rid of him and have healthy, happy community fish, or keep him with tired worn out and fatigued fish.
As for the snail problem, I don't know why I didn't mention them before! *slaps forehead* They sell them pretty cheap in my LFS, but a while ago I went into a branch of Pets at Home and they were giving them away as pests to be fed to puffers etc. If you know what you're looking for, and google a good picture, you might get some free! Dwarf chain loaches are pretty sweet too, although they don't seem that active whenever I see them in the shops. When I was starting out I had a Pakistani loach, or YoYo loach as its sometimes called. Striking colours, endlessly active in all levels of the tank. I'm told they should be kept in groups and can grow to over 5" but the LFS that sold it to me all those years ago was adamant that you should only keep one... Hmm, perhaps I should research this a bit more before giving advice. Argh, I'm rambling!