Need Help with Staghorn

Ok.... I have staghorn growning in the tank. It started when I left the tank alone for three weeks over winter break. I came back, removed affected, and started fertilizing. I even bumped the CO2 up to the point where my plants are pearling (which is crazy because I have a large bioload and surface agitation from a HOB filter). The staghorn is still growing, both in sections where I didn't remove all of it and on some new growth. I am dosing using the proper amounts as given in Chuck's fertilizer calculator. Water circulation is good, CO2 is being diffused using a glass diffuser and then bubbles get chopped up with a powerhead. What should I do?