My Betta and I are in a bit of a fight. What started out looking to me like a small cut or abrasion (see photo 1) in January has ballooned into what I think is a large puss filled abscess, although I am not positive and would like a second opinion. I have never had a fish get this problem. It started off pretty gradual but it is getting larger much quicker in the last month (photo 5 was March). I am a bit unsure how to treat it or if I can at all. This fish is in a community tank and I started him on a course of meracyn in a quarantine tank in January but after a week I decided he was more stressed out in the quarantine than in the aquarium as he was not eating, hiding, and refusing to approach the glass when I came by (which he always does) and the cut did not seem to improve at all). Do I attempt quarantine again, stressing him further and if so, do I try maracyn again, salt, or some other medication? I am also unsure if I should try to lance the wound so it doesn't burst and create a large open wound. Water conditions are pretty stable. I just did a 50% water change to see if that would help at all, although they haven't seemed to help much over the last few months. All other fish, shrimp, and snails are fine and acting normally including breeding so I don't think its something tank-wide that is off.
Ammonia: 0ppm
Nitrate: 10ppm (haven't added in Easy Green yet as I didnt want to throw off test)
Hardness: between 75-150ppm
Chlorine: 0ppm
pH: 6.8ish