The tank is in my garage, and without the heater the water temperature got to about 45deg. They were dying at a higher rate at the lower temperatures, about half what I bought were gone before I could use them. With the heater, which is set for 62deg, I rarely loose any of the feeders (its typically 1 out of 30 feeders). Since I keep them 1 month before feeding, I want to ensure they will live long enough to meet there death in my large tank.