I really dont think your going to give your other fish any thing from that it looks to me like a tumor,somebody correct me if im wrong cause im not 100% on that
cant really tell from the pics, but but I know they dont have raised red bumps, so no its not suppose to be there. Not really sure how to treat it but I wish you the best of luck
Salt might work but be careful he is scaleless. It isn't supposed to be there. Maybe give it a bit in really good water quality and see if any changes occur. Maybe it's a reaction/hive/irritant manisfestation. You did say it came from very poor water. It's always best to deal with water first and not treat unless you know for sure or nothing else works.
1. Tumor or cyst. Infection from a wound that is being covered by cyst.
2. Tranquilized the fish using clove oil or ice. Cut it open and and remove the cyst using a cotton swab soaked in a small amount of water with antibiotic+salt (use just enough water to disolved the antibiotic and salt). Make sure to removed all dead cells from the wound. Then Put the fish on a quarantine tank with 500mg/20gal of broad spectrum antibiotic. After two days change half of the water and add same amount of antibiotic again. Do this until the wound heals. But if you notice that it's not geting any better after the third treatment do it on a daily basis.