I tried this recipe often seen on FB some weeks back, barely worked. Late yesterday I sprayed the rest but this time as a coarse vs. fine spray so I could get the sprayer empty to next try ZEP Shower and Tile Cleaner based on glycolic acid made from sugar cane...even though it rained lightly and briefly about 2 hours after I sprayed, today, 24 hours later, the amount of browning is very encouraging.