White spot?

So I had a a redtail shark and a columbian tetra struggling with a white fungus or something. Redtail shark is completely better...The columbians head has gotten blackish and rough looking and a white spot is re-emerging. I also have a black skirt with a spot on its side. Any thoughts? They are still eating some as well. I had used Melafix and took out my filter media because I was told it would suck up the medicine. Well this caused me to lose 5 fish. Here is my question and Finley you might have the best input. Would salt work for this and could I leave old carbon filters in there just to filter the water? The carbon filters are over a month old now I believe and I was waiting till after treatment to change. I know new carbon will counteract medicine/salt but with older I was assuming that they might not take away the medicines usefulness.

I use salt and garlic for all my fish illnesses and injuries and works for me!I never buy meds from the store! Also raise the temp to around to 86 degrees!