Why, Ryo... WHY!?

[Findlay]

Hey all!
So, one of my guys (Ryo, the VT) in a divided 10gal is having fin issues.
I am thinking it is a case of *tail biting*.
He just finished up some AQ treatment (for a small rip that was there where I got him), and his fin was looking great
I put him back into his side and a few hours later - I noticed his fin (caudal) is looking raggity and ripped.

There is NO possible way that my other guy coulda got to him, my filter is baffled to perfection, there are no dangerous decorations/plants, and the water chem/temp is normal/steady.

Is it possible that he just CAN'T be in a divided tank?
Could it be that he's just a sissy and maybe there's too much stress being near another male?
Help?

Siiiiigh... I hate to have to put him in a single tank, but I'll do it if he needs it <3
I'll try to snap a pic of his fin, so you all can see...

[Findlay]

Alrighty --
The first pic is of before... his caudal in A+ shape...
The second, if you look closely (sorry, it's the best I could do!) you can see a bit of the damage...
And the third pic is just for fun I thought it was a good pic and wanted to share hehe

What do you think I should do?
Thanks!!

[Findlay]

I would really appreciate any help or advice!

[Tikibirds]

My guess is the other fish is stressing him out. maybe try putting plants along the divider so its harder to see his tankmate?