The most common reason a scoby grows mold is the lack of starter tea. Starter tea is what lowers the ph of your brew making it safe. Starter tea also contains all the beneficial bacteria that will grow a new scoby. We recommend using 2 cups (16 ounces) of starter tea per gallon of sweet tea, this will ensure a new healthy scoby grows. For your batch that molded, you will need to toss it out and start over, this time use 16 ounces strong starter tea!