I wouldn't jump to any conclusions too quickly. My old Dempsey has a (presumably) genetic disorder which resulted in complete loss of swim bladder control. I tried every many medications, but nothing helped. He is still happily living on the bottom of the tank (soft sand) even a year later. He still eats and swims fine, but when not moving remains on the bottom of the aquarium. He got smart, and props himself up in the fake plants.
I talked with a vet once who said that it's likely a genetic disorder due to improper/poor breeding. I acquired the fish back before I started buying from reputable breeders, so it doesn't surprise me.
In your case, the rapid degradation may indicate something other than genetics. Try the salts an medicated foods first. Maybe increasing the temperature a couple of degrees will work it out. I would just make sure that the fish is eating. Make sure the food (sinking) gets close to it, so it doesn't have to move much.