Best treatment for oscar?

[Donkey]

I got this little oscar yesterday from someone I work with.   He told me about the fish so I offered to help him treat it in my quarantine tank.  Unfortunately, he doesn't know the water parameters.  He just said he got it at a pet store a couple months ago, and it hasn't really grown much in that time.  Within the last couple of weeks he started to notice what you see in the picture.   The fish is still fairly active and eats at least a little food every day.   

I am guessing there is some fungal infection or something with the way the fins look and discolored areas of the fish.  My coworker also recently noticed white stringy feces which you can see in the picture.   I hastily dosed some metroplex yesterday, but now I'm second guessing and think I should just use salt and prazipro or something similar.  I have both prazipro and general cure on hand. 

Would salt and parasite meds be the best option?   He also said he had another oscar and two angelfish that he got at the same time.  I'm going to try to convince him to let me go ahead and treat them all.    I told him they weren't the best tank mates, and I will help him with that after treating.   Thanks in advance. 

 

[Colu]

I would treat  with prazipro and aquarium salt 1 table spoon for 2 gallons  for the fin issue if the fins get worse then I would treat with kanaplex his fin look damage from fighting rather than fin rot  with salt and him being on his own should heal in a couple of weeks