Can you pick up potassium permanganate from the chemist?
A rather bizarre tx but I've seen it used again & again with (poorly) discus & it really does seem to help them
Simply Discus has a reprint of the UF EDIS article
Use of Potassium Permanganate to Control External Infections of Ornamental Fish
Ruth Francis-Floyd and Ruth Ellen Klinger
Seachem ParaGuard can also be used, as a bath most commonly, but in this instance I'd follow the directions for a short term dip, followed by "bath" conditions in the tank
You can expect this fish to lay down in the "dip", monitor respiration as stress signs
Set up a bare bottom hospital with a simple air driven sponge filter, filling water initially to about 18-20 cm
If fish is able to swim & remain upright (there is stress "laying down", then there is "can't get up & maintain equilibrium" laying down), you can slowly increase water depth, checking that fish remains comfortable
Water temp should be at least 31 - 32C, low flow(planted tanks are really only for healthy Discus), daily water change (90% if possible)
The bare bottom will allow you to monitor food consumption & waste production etc
This container should be only ~ 35-40 litre - ill/stressed discus won't move much & seem intimidated by larger tank spaces
Use a large sponge that fish can hide behind (maybe run 2 sponges in tank)
Tank should only be dimly lit, but as discus can startle badly, especially when alone/stressed/ill - keep a "night light" on
If you can't do Edvet's live food (best possible for this fish!)
Offer food that fish can eat overnight rather than expecting fish to eat a decent amount upon offer - freeze dried Australian black worms would be my first choice (you'll need to see what's available & what Discus will eat ... frozen Hikari bloodworms (very "clean" brand) may work as well but degrade in the warm Discus water
I'd not offer any beefheart foods until fish is eating & pooping well (bh is popular as it puts rapid size on discus juveniles but it is not the most easily digested)
(I'd personally never feed beefheart to any fish but that's a whole 'nother story )
If you've already added this discus to your planted tank with other fish
, you'll need to choose which way to go ...