Why would ventral fins curl?

[labloverl]

I have a VT that had straight ventral fins when I got him. He's in a divided 5 gallon now and I've noticed that his ventral fins look deformed. They don't actually curl, but they kinda form an "L" shape at the ends. Could it be the small space of the divided 5 gallon? I've heard that CT rays will curl in hard water, but what about VT's?

[MyRainbowBettaFish]

i beleive it can be caused the kh/gh water hardness

[labloverl]

Is there anything that can be done? My other fish have never had a problem, even CT's.

[Silverfang]

I believe genetics, previous fin damage.. just about anything really. I've had it in a couple of fish. My water is soft as can be, 7-7.5 ph. They still got curling and kinking.