Yes, if you have mildew stains that have formed black spots or patches on your patio then you can use chlorine bleach and water to get rid of them. However, you’ll need to take care and make sure you dilute the bleach to a safe level so that it won’t kill any nearby plants or be harmful to wildlife, children, or pets in your home.
Mix one part bleach with two parts water in a spray bottle and spray onto your patio. Alternatively, you could use a bucket and a mop to spread the solution.
Leave it for 30 minutes and then use a scrubbing brush to remove the black spots. Then rinse it off with your yard hose, taking care that the solution doesn’t touch nearby greenery.