Everything we used to clean our limestone front steps (and my fall outfit from the reel). Here’s how we cleaned them. This could apply to other stones but make sure to test out first. 1) pressure wash - the Ryobi one is a great value 2) spray and rinse with Zep concentrated pressure wash cleaner 3) use a soft scrub with dish soap mix with warm water - although it didn’t get out the algae + mildew, it helped a little before trying the bleach solution. some people skip this and go straight to bleach but i wanted to try out 4) for stubborn stains, mix 1 part bleach with 2 parts water and spray on. bleach is safe for limestone but test this in a small spot first to make sure it won’t damage your stone. leave for about 1 hour and rinse. 5) allow to completely dry before sealing with Rain Guard Sealer using a garden sprayer to protect from moisture, mold and mildew. LTKHome LTKSeasonal LTKStyleTip