Discuss with white skin rot Help

[Pimpintacoma]

I have a Discus a tad sideways and larger white skin rot. I need help from the pros on the best way to treat this to save his life. He is my pride and joy. I also noticed he is a tad darker than usual.
Ammonia is 0
GH is 50
Free chlorine is 0
Nitrate is 25
Nitrite is 0
Carbonate is 40
PH is 6.4
Temp is 84
120 gallon tank
Two large canister filters
One top filter
Use RO for water changes about 20% weekly.
Use prime in water.

So far I moved him to a 10 gallon quarantine tank and added two rounded table spoons of salt and bumped the temp up 2 degrees over a half day.
I would like to know a recommended treatment.
I plan to make some RO water and do a few 50% water changes and maybe add some salt. Please let me know what you think this is and what my best plan of attack is. I don’t want to lose this fish.

 

[Brookster123]

Something with the water. Gills look severely agitated. Need to know more about the tank. Stocking, age.. all the details. One thing I can throw out immediately. If you're only doing 20% changes with ro than you're really not helping at all. Unless your tap is absolute liquid garbage, you'd be better off with a 60% wc using heated/treated tap. Are you buffering the ro water? These domestics are, more often than not, bred and raised in tap. Ro is more for wild types and breeding.

 

[Pimpintacoma]

1 year old tank moved from a 60 gallon tank.
I have
5 discus
2 angel
To of glow tetras
And a few other fish pictured
Algae eater
Tap water has seen TDI of 350+ and also 120 and less. So I switched to RO just so I didn’t have to battle with chemicals all the time to fix the numbers.
Never really had any sick fish issues with all this setup.
I only use Prime in the RO water and always had good numbers and consistent numbers.
Only twice have I ever used alkaline buffer and acid buffer to get to a PH that I wanted.

 

[Brookster123]

Jeezuss... that stocking is all wrong. If I had to pick the worst possible tank mate for discuss... you have a bunch. Everything you're doing is wrong for discus. They are a sensitive fish. I cannot offer any advice other than to prioritize your wants when it comes to keeping fish.
Anyone can have discus, not everyone can keep discus.
Sorry if this came off as harsh but I am actually offended by that picture of your tank.

 

[Pimpintacoma]

I have thick skin so no harm in telling me what’s real.
3 of the discuss are 3 years old and the other two are over 1.5 years old. Not sure that’ means there is an issue.
They all seem to thrive and act correctly.
If they were in a poor setup I would have had issues over the past several years right?

 

[Brookster123]

If they made it that far.. feed em a steak and make peace??

 

[Pimpintacoma]

Not sure what that means

 

[Brookster123]

Nothing. I'd treat with bacterial meds. Clean clean water.

 

[Pimpintacoma]

Any type brand specific?

 

[Brookster123]

Start with api erythromycin