No, it’s not safe! Throw the tea and the SCOBY out immediately. As for why this happened, there are a couple of possibilities. Sometimes people do not follow the recipe exactly, throwing off the ratio between the ingredients, which in turn throws off the fermentation process. Be exact in your measurements. The other cause can be airborne molds in your home. A few people I know developed this problem because of a leaky roof or because they placed their pot of kombucha in a closet that had poor air circulation.