I would probably use aquarium salt..Epsom is mostly used as a laxative for bettas and helps with bloat.
This website is helpful in understanding the lifecycle of ick.
The aquarium salt helps with keeping away infection when they cysts fall off. Once they fall off they die in 86 degree water temperatures...I leave my heater at 86 for a few weeks. My tank is now ick free. I would stick with one method though, sometimes combining meds with the higher heat can stress fish out.
Why did you turn the filter off?
Is there anyway you can get a photo of your betta?
I apologize if I am making no sense..I have only had 2 hours sleep. haha
It may be possible that the medication is having a bad side effect with your one guy.Was he acting ill before you started treatment?