My Roses Have Terrible Black Spot; Help?

Black spot can be caused by several things, insects, fungus and soil pH imbalance. In my experience it is usual an insect. My preferred treatment is Fertilomes' 3n1 insecticide, fungicide. It is different than the 3n1 you're using, i.e. it does not feed the plant and the insecticides are different. The fertilome 3n1 can be used as a systemic and topical treatment. I use it both ways for 2 weeks, then only as a once per month until the plant has new growth and shows no sign of damage in the new growth. I also insure that the underside of the foliage is wetted with the fungicide. It will take at least 2 weeks for the plant to show signs of recovery. During recovery I use a balanced, water soluble fertilizer at 1/4 recommended strength applied about every 3-4 days.