Mix a solution of 1 part chlorine bleach to 1 part water. Fill a spray bottle with the solution. A bleach cleanser, such as a bathroom cleanser, can be substituted, but those typically have a lower ratio of bleach to water.
Spray the stones until they are thoroughly damp. Start in a corner that is out of the way to test the solution.
Scrub with a hard bristled brush until the liquid begins to darken and appear grimy. Rinse thoroughly and inspect the stone. Stop using the hard-bristled brush and switch to a soft-bristled brush if the stone begins to appear gouged or scratched. Complete the remainder of the patio and rinse the structure thoroughly. Allow to dry for 24 to 48 hours.
Spray the surface of the patio with a concrete sealer using a pump sprayer. Hold the nozzle 12 inches from the surface of the stone with the nozzle set to a wide spray. Spray with broad, even strokes until the surface is damp with the sealer.
Brush the sealer into the stone with a wide-headed broom.