Floor Mildew?

Go to the store in the floor wax section. Buy a bottle of Wax Remover. I use it on my floor for the bad areas that are hard to clean. Pour alittle on, let it set for several minutes and use a scrub brush, if the corner is tight, use a old toothbrush and maybe a single edge razor blade to scrap it off. Then keep it washed down with alittle bleach each week.