I would suggest next time you do a water change, take the water level down so that the affected plants are exposed to air. Get a large paint brush and brush Prime undiluted directly on the algae and the affected leaves. Then refill the tank. Adjust your ferts and CO2. Change one thing at a time and watch to see if the algae goes away completely. At worst, you may have to remove the affected plant. Prime works just as well as excel, just not as toxic.
Amanos will eat BBA after it turns red, not so much the staghorn. Continue to change the water every other day for the rest of the week to get rid of the dead algae. You won't see it, but there are plenty of microscopic debris in the water column after these type of treatment, and that alone can skewer your tank towards growing more algae. GL.