i use hydrofarm thermostat. It's weird because the day I got it and used it the 4 days the temperature was at a constant 88-90 when it was set at 92. After that it started going down to maybe 87-88. One of my tubs is staying at a constant temp but the other tub the temperature is like 87-88 and then today it went down to 84 when it was set to 93. The other tub is still 88-89.