The other day I was browsing a pet store (Won't say which) and I came upon a betta fish that was in the WORST condition I have ever seen. I picked up the fish cup with the dirtiest water. He is a beautiful duel tail betta fish, except his fin rot, pop eye, and whatever else he has. My heart immediately dropped when I saw the condition he was in, so bad that the store adopted the fish out to me for free. I figured the fish at least deserved clean water. Anyways, it's been a couple of days now, and I've been treating him with Melafix in a hospital tank. I already did a huge water change. It seems like he may be getting worse, and I'm scared he won't survive. :( I have no idea what is wrong at this point, or why the Melafix isn't fixin' the job. It seems that his face is deteriorating. (I'll insert images) Above his mouth there's a line across that's pretty much see through, may even have holes in it, because of how bad he's deteriorating. Also, on his eye with pop eye, there is redness underneath that seems to also be deteriorating. He has fin rot on his tail fin and also on the fin underneath.
As for how he's acting- he swims around a bit, won't eat (though I don't blame him with his mouth wounds), and occasionally tweaks out. o.0 Mostly he will just go up for air.
Please someone help me figure out what's wrong or how to make him better. :(