Brian I am no discus expert, but have been in the hobby 38 years. When dealing with intestinal blockages in african cichlids the mag sulfate dose is 1 (sometimes 2 in bad cases) tbsp per US 10 gal. You wrote 1 tbs, but didn't describe per what water volume. It looks like a blockage or mass of some sort. If it's a mass, I do not know how to treat it. If a blockage go up on your mag sulfate dose to 1-2 tbsp/10 gal and increase the water temp to stimulate a higher metabolic rate, and make sure you have good aeration as higher water temps mean lower O2 carrying capacity. I hope it works out. Looks painful...