I have three tanks and 4 brand new non adjustable heaters. Before I got my two Bettas I had the tanks set up and heaters plugged in, one did not work, so I took it back out. Two were holding right around 80 which I thought was great. those are the two I am using. The one in Clive's tank is now reading with temps over 80, maybe 84, 85. I want to get a good mini heater for my tanks that I can adjust, so brand names or links for those would be much appreciated. (I did type in adjustable heaters in the search forum, but that gave me too many posts to go through to find what I needed!) In the mean time, the heater in my non fish tank is reading consistently 77.9, would you recommend I switch out the higher running heater for the lower one until I can order something else? Thanks for your help!