If theyre bumps then it sounds like a parasite, which salt and raising the temp. would help with. I dont like saying go for a med, but if its getting worse you might have to use something. I would suggest trying a Formalin treatment (its getting harder to find pure Formeldahyde, but its the safest med for fish) but you can use PondFish treatment by Tetra, or you can use a zinc free Malchite green but make sure its zinc free!
With that being said, I would try salt, heat and large water changes (30% or more) every other day or so to start. The small changes might sound good, but there was an article put out in TFH a few months ago saying that they arent as effective as we all hoped they were. And for sure keep a close eye on all your other fish, not so much for aggression as for symptoms. Maybe even adding a Garlic supplement to your fish's food would be a good idea, the Garlic acts as an immune system booster.
