Iron chlorosis, for example, is often treated by adding large amounts of chelated iron supplements to the soil. In this case, the symptom is yellowing leaves with dark green veins (leaf ribs). The cause of iron chlorosis is often high soil pH - a condition which traps existing iron in the soil, and prevents its use by the rose. The treatment, therefore, is not the application of supplemental iron, but rather the application of organic materials to bring the soil back into natural balance or slight acidification.
I just got a pH meter. I have seen them at Home Depot and Lowes for under $10. Mine measures pH, moisture and light levels. You have to get the soil muddy or put it in a container and add water to test the pH. Maybe that will help you figure out what is wrong with your rose.