Mark,
Welcome to SimplyDiscus. I wish it was under better circumstances. It looks to me like your fish is at the end of its life. The not eating and wasting away..the leathery wrinkled look to its sides.. 8 years is a long time for a discus.. most hobbyists usually keep them alive far less than that.
The white mass could be from an infection.. older fish have weaker immune systems. It could have gotten blocked up as well. In the video I can see some swelling.
I wish I could suggest some miracle medicine here but best I can do is suggest compassionately euthanizing it..
I really dont think medications will help and at this point its organs are probably shutting down.
Im really sorry.
Al