Review on Aquarium Submersible Temperature Intelligent Controller by Marie Burris

This heater is incredibly inaccurate, the measured temperature deviates by at least 6 degrees from the actual one. I run a temperature controller with this unit as well as a traditional thermometer and both read a much lower reading than what the heater thinks. I have to set the heater higher than I want and even then it struggles to heat the 9-gallon tank. I need it to reach 73 degrees, indoor ambient temperature is about 65 degrees at night in winter. The suction cup also refuses to stick to a freshly installed tank. No matter what I do, it will eventually pop out of the tank. While the external control is handy, easy to set up, compact in size, and space in my tank is a big deal, it's a shame the rest of the heater doesn't work properly. There are no instructions for recalibrating the heater.