His fins were growing back so nicely too! Grr. He took a chunk out of his caudal fin and now it's all wirey and split. It's not terrible, but it doesn't look good.
I took his plants out for the time being to give him room to swim and heal, and I'll be making a pet store run at some point tomorrow to grab the salt to prevent infection and all that jazz...
Anything else I can do to prevent this in the future? (I never have ANY problems with the other three, it's just this guy! FRUSTRATED.