That does look like a red devil to me. he's pretty long to be a midas IMHO. But if you got him in a common LFS that doesn't keep pure breads, he's likely got a bit of red devil and a bit of midas in him.
Yeah man, that's one of the nicer black belts I've seen.
If I lived in FL, I'd be happy to help you "thin the herd" and take that black belt off your hands hahaha.
Good to hear you've taken it upon yourself to learn about proper nutrition, and got rid of the HITH. The jag looks pretty nice too. But for as old as he is, he's a runt haha. Should definitely be above 15" at this point.
Honestly, though.....I don't know how that stock is working so well for you. I'd have figured the jag would have killed everything in there. Same with the red devil, and as he gets bigger, I'm sure he'll start tearing into the other fish. In only a 4' tank, one of them is likely to start thinking he'd be better off being the only fish in that tank and may start killing off the others. Eventually, you'll have to get rid of some. You've got 2 fish that get real big, and a few others that get pretty big. A couple of those could definitely use that entire tank for themself once large enough. Anyway, it's all been said in previous posts. Just keep an eye on them, and get rid of your least favorites as the fish start getting too crowded. And keep up on those water changes. I'd just make it routine to do 50% 2X per week on that tank, and do some Ammonia/Nitrite/Nitrate checks every once in a while to make sure things stay in check.