Long ago I read a very well-written article on how high temps will kill the bacteria in the tank and cause it to recycle. In the article, it said it starts to die around 83F. I have been pretty paranoid since I have also when my tank spikes my skimmer gets very active. So this is my first year with a chiller and I am very pleased with my purchase, the tank has stayed right in the range I would consider being safe.