In a 150 gallon tank there's an aro about 1.5' long, a pink convict about 4" and a pleco 7". The symptoms were there before he placed the con in a month ago at least. The aro fins (all of them) were damaged and rapidly disappearing. I asked the owner if he was treating the fish, he said yes, but I went back a few times over the last couple months and he's been worse. Now, the aro has NOTHING for fins but the nubs that the fins were once attached to and the con is the same way. It looks like there is a hole appearing on the tops of both their heads. I felt so bad I wanted to take the "show fish" home. 
Only the pleco seems unaffected. I think he had something else in the tank before the convict which also disappeared. Can't remember what. It had been almost a month since an h2o change. I told his employees to do 50%. I keep telling myself I'll bring a camera but face it, I don't remember 'cause there aren't any cool fish really. He doesn't know what's causing it all. Help the aro!
What's causing this?
Only the pleco seems unaffected. I think he had something else in the tank before the convict which also disappeared. Can't remember what. It had been almost a month since an h2o change. I told his employees to do 50%. I keep telling myself I'll bring a camera but face it, I don't remember 'cause there aren't any cool fish really. He doesn't know what's causing it all. Help the aro!What's causing this?