Encountered this phenomenon in General, you can make a decision, that is, whether it would be saved, there has been the trend of expansion, if there is, it is advised that you might as well get off a, playing again with a layer of plastic glass; if status is OK, then you can try the following methods. Firstly, find a used toothbrush, dip a little laundry detergent, using the most primitive methods-Cleaning mildew blackened, although very unusual, but certainly much better than cloth, is a little effort; if you have trouble, you can then see the next method. Take paper towels, 84 liquid disinfectant, torn black border size as much as possible, dip a bit of 84 disinfection solution, and then you can tile directly on mildew, then wait quietly, generally takes 24 hours, although a bit long, but it is very simple, no trouble, and lazy for Oh! Highly recommended!!