Sick Discus - Looking for Treatment Advice

Sorry if this is a repeat thread, had some technical issues with my first post so not sure if it went through.

I have a discuss that has been sick now for 2 weeks. I tried doing 5-10% water changes over a string of days but he doesn't seem to be improving. He is now hiding in the back of the tank and not eating.

Can someone help ID the disease and help suggest a treatment. Parameters are fine: ph, temp, ammonia, nitrate. All the other fish are fine but this is the only discus I have. Tank is heavily planted and has a canister filter with bio media in it. Tank itself if 7 years old with no historical issue of disease. Hoping there is a way to treat the tank as I don't have a viable option for quarantine. Also I am remote (this is a tank at my business) so I need to give directions to my staff to help solve.

Sorry to hear about the problem with your discus. For me, this one is too far gone and needs to be euthanized. It was not the best fish in the first instance as it was badly stunted, so initially it was going to be on the back foot. The sunken head above the eyes the clamped stance and velvet look to the skin as well as the cloudy eyes scream to me to end it's suffering.

Causes.. it has been like this for more than 2 weeks imo, probably not eating for a month at least an just picking and blowing out food. How many other fish are in the tank? more discus too? You say that your water is ok, but what are the actual values? What temperature is the tank at? Discus prefer higher temps 30 degrees is best, but this is not always good for tank mates. What other tank mates are there? maybe he has been bullied by fast moving, nippy fish. Water changes of the amount you have mentioned do not bode well for a healthy environment. Discus can be prone to bacterial and parasitical build up if you do not take care to give them the cleanest water conditions. I would be changing 40% two times a week at least. In a planted tank uneaten food can be a problem, if you are not vacuuming the gravel, leaving areas of anaerobic bacteria to create toxins that will poison the fish.
A tank is environment is only as good as the filter, running for 7 years does not necessarily mean it is healthy, please test the water in the first instance and come back to us. But for the fish, it is so sad to see, and ending its suffering is a wise choice.

H