Ich is usually brought on by stress, goldfish are very messy so it could very well have something to do with the water paramaters. If you can grab a water sample and get numbers for ammonia, nitrites and nitrates that would be very helpful.
Also, about what size tank is this and what sort of goldfish? I wouldn't keep a single fancy goldfish in anything less than 30 gallons, maybe 20-25 gallons for one of the smaller varieties like the bubble eyes. Commons and comets need much more space, wouldn't go under 75 gallons for them though a pond would be better. If its a smaller tank, he's likely been stunted by poor water conditions as they do stunt very easily.
As for treating the ich, I would not treat him like a tropical fish, they prefer cooler temperatures so I wouldn't go as high as 80F, try 75F but only if the tank is well aerated. I'd also suggest doing a good water change, 20-30% with a very thorough gravel vac. If they're medicating the tank and it has activated carbon in the filter, the medication is being removed before it can do any good.