Idiriscent Shark

Question
I'm glad to have found your website, but unfortunately i have not found any cases similar to that of of my Iridescent shark.  I live in Florida, and during the winter the temperatures of the aquarium do not drop below 20 degrees Celsius, currently the aquarium has that temperature. The first day that a cold front came through my area the temperatures lowered to the temperature it has now(20 degrees Celsius), this first day, though, the iridescent two sharks that i have, their  skin( i guess i could say since they seem to not have scales) seemed crack as if it were frozen, but they weren't frozen. Anyways, the next day one of the sharks had one cloudy eye and the other had both of its eyes cloudy. The shark with both cloudy eyes also had red streaks under at the base of the pelvic fins. All the fins of both fish (dorsal, caudal, pectoral, pelvic, ect.) also became teared, and are all stringy. The worst part, I consider, is that the shark with both eyes cloudy seems to be blind and can't really find its food (flakes). As for the aquarium, I maintain it very clean and the treatments i use  are Aqua Safe(neutralizer), algae destroyer weekly, and Easy Balance weekly(chemical balancer). I clean the aquarium yearly, with 25 to 50 % water changes every two or 1 and a half months and monthly filter clean/change as well. The Aquarium is well-oxygenated and I feed them daily. Currently, the heater is on and it maintains a stable temperature of 20 degrees Celsius. I also vacuum the gravel monthly with the siphon.
       I really hope you can help me in determining the disease of my iridescent shark, and informing me of any possible way to treat it. If you need any further explanation, pictures, videos, or description e-mail as soon as you can, this is very urgent and i've had these fish over seven years and i would greatly appreciate your help. Thank you for your time.  

Answer
Your temps are WAY to low, they should be more in the area of about 76 to 78F, your currently at 68F and that is just plain  to cold!  Your sharks are suffering from a bacterial infection due to incorrect conditions, treatment should be as follows, increase the temperature to 78F, add 1 tablespoon aquarium salt to one gallon of water, in 5 days to a 20 percent water change and in another 4 days do another 20 percent water change, at this point you can go to standard weekly water changes of 15 percent, keep the temps in the 78F area and do not lower them or you risk another outbreak.  Make sure your using a good water conditioner with each water change.  Also stop using the easy balance, its they type of product that will cause an unstable PH and stress your fish.  Good luck.