There is a book for you to find that will give you an idea about the potential for disaster when using Potassium Ferricyanide. It is called, Overexposure, Health Hazards in Photography. You will see that mixing any acid with Potassium Ferricyanide produces cyanide gas, not really a good thing for a long career in photography, albeit a small concentration. You do not need to use fixer, it is an old school way of getting the bleach to act faster (it becomes an accelerant). Be sure before you put your print back in fix after bleaching that you rinse it very thoroughly with water or the residual will suddenly act up again for the same reason. I agree with Aggie fully too, you need to start slowly and patiently, you can always bleach some more. Of course, wear gloves and have ventilation.
Take a gander at that book too though, it's a good thing to have as a reference in any photo library...
Good luck, Ray