Oh No! Its been one day, and already, shredded fins?

[coolcucumber]

Well, my veil-tail chocolate betta has been released into his split tank for about 1 day now, and has already managed to shred his caudal fin. I have no idea how, which is why this is bugging me. The only two ways i can think are the filter, or the divider. But, i covered the filter with a stocking exept for a tiny bit at the top i couldnt get, so it seems highly unlikely, especially because he used to have free reign of this tank WITHOUT a stocking covering the aquaclear filter intake.

The divider is a lees divider: Amazon.com: Lee`s Aquarium Tank Divider 10gal: Kitchen & Dining

it has small holes, and apeares to be a thick plastic mesh. but, i dont know how he could have hurt himself on it, because its thick, hard plastic with alot of holes.

So, im a bit confused. Hes in a vase which is floating in his half of the tank, with aquarium salt. not sure what else to do until i diagnose this, but i dont think its fin rot.