Um, I could be wrong, but the edges of his fins in your first picture look brown, which means finrot, and would explain the missing bits in his tail you described... Make sure to keep his water super clean if I'm right :D
on his tail, it looks more like he bit it. if it were fin rot, it wouldn't be just a few chunks missing. my Dante bites his tail, and the first time, it looked alot like this fella's. on his top fin, however, that may be fin rot.
Well the coloring on the edges of his tail fin had a black line around it, but since his tail got a little scraggly, it's hard to notice.
But I will do water changes more often and hopefully he won't get any worse off.
I will try and get a "flaring pic", but he is so laid back and not very aggressive, maybe that's just because he hasn't seen himself yet.
As for the fin rot, there might be a little bit on the dorsal fin, I did about a 90% water change and will keep up maybe 75% twice a week, is there anything else I can do?