i have used "chemiclean" red slime remover with success. if you've been doing repeated water changes and can't get rid of it, this product should work for you.
just follow the directions and you won't have any adverse reactions.
btw, this is "chemiclean", made by boyd enterprises, not to be confused with "red slime remover" which is an antibiotic called erythromycin.
ultimately, it will come back if you keep a high nutrient tank. you have to take out what you put in or you are going to end up with more trouble than cyano