How do you use the muriatic acid because I am having some problems getting rid of oak pollen stains?

When using Muriatic Acid it's important to wear the proper protective gear, and have plenty of clean water on hand in case of an accident. Always pour the acid into water, and not the other way around. Wet the stones before cleaning. Dilute the acid with water. Make sure the stones are soaked with water before applying, and don't leave the acid on too long. Scrub the stains with a scrub brush. Rinse everything off, and allow to dry.