What do you use to remove stains on your deck from mold/algae? We tried boat soap/deck cleaner, scrubbed with a hard brush, but it just doesn't want to come clean. It is on a 'non skid' deck. Should I use bleach, or go with something like mildew stain remover, obviously I don't want to do anything to hurt the fiberglass deck. It is an old boat, '78'. ?????? Thanks.