Guide to Betta Disease

Bought him 1.5mth ago, added salt into his water for almost a month, but his condition didnt ease nor worsen. it doesnt look cotttony, more of discolouration and greyed out? He's red btw so it looks very bad.

Any idea how to treat him?

He's eating normally and active, blowing alot more bubbles as days pass. Just that he swims funny when turning on the direction of his infected side.

Unable to post pics as i'm new to this forum...