Sick Iridescent shark

Question
Can anyone help with a diagnosis/treatment for a iridescent shark? I have a photo, which is a little blurred but clearly shows what may be GBD? The tank is a 50 gallon, once a month water change, water is aged, heated overnight and dechlorinated. Water temperature is 80 F and fish are fed with flake usually.

Answer
Hi Mark;

Send your photo to;

AllExperts_Fish_Guru(a)yahoo.com

Also please include the following info;
How big is the fish?
How many other fish are there?
What kinds and what size are they?
How long has the tank been set up?
How much water is changed when you make changes?
How often is the gravel vacuumed?
How often do you feed them?
How long does it take the fish to eat all the food?

At Your Service;
Chris Robbins