The Dissolving Betta...?

[Peep]

But the tank is divided into 2 with one of these, thought there would be enough room for him to get away from the screen...

http/www.rocketaquatics.co.uk/penn-plax-tank-divider-p-4368.html?osCsid=a7fntstqinv20sm26knuao9n84

Also may be a bit of a newb thing to ask but I don't get why his fins are still breaking off when the other beta definitely hasn't been able to get to him for 24 hours. Is it the stress?

 

[Alm0stAwesome]

You didn't mention any of this in your original post. What fish are in the tank in total, and what do you have on each side of the screen? Because you've got no room in there at all with this tank divided like that. Sounds like a recipe for disaster if I'm honest with you. Also, some bettas do something called tail biting when they are bored or stressed. It's hard to say without seeing a picture of what the damage is