There are several factors that can affect SCOBY growth. Cooler temperatures - in your region, your air-conditioned home, or your refrigerator - can significantly slow fermentation. Make sure your kombucha is fermenting in a warm spot - 80°F is ideal. Lower ambient temperatures may require longer fermentation times.  Quality of water also matters. The chlorine in tap water can damage or kill cultures, so filtered water is best.  Make sure the tea you add to your batch is cooled. Tea that is added when hot can damage the SCOBY, resulting in inactive cultures.