Right now I have 2 diffusers, the one in deep end hardly puts out any bubbles compared to the one in the shallower end. The deep one is in 8 ft of water and the shallow one is in about 4 ft. I guess I can just monitor my water temps to see if it's cooling too much. I'm sure the aeration isn't necessary in winter, but I was wanting to continue to run it to help with the bottom muck as long as it won't harm my fish.