My husband and I bought our first home in March.... I have recently noticed the Tank sweating [badly] which normally would not bother me so much until I was scrubbing the floor and was down scrubbing behind the toilet and noticed black mildew on my white tile. I could not get it off , I used Lysol with Amonia, the works and so on.. but yet there it is on floor BLACK MILDEW! Does anyone have any id's or reasons why this is on my floor and how can I safely remove it without having to rip up my floor. All advice is greatly wanted.