I recently got my aquarium set up after a long time due to home moves.
One thing I noticed since then is that the new digital temperature thermometer I got for it seems to indicate that my aquarium heaters have always been inaccurate.
I have a Tetratec 150w and 200w heater. They seem to heat the aquarium water to higher than I have selected on the heaters so I think that the thermostats in these heaters must have never been very good?
With the warm weather we have been having recently in the UK I have not needed much heating for my aquarium as it is already at the temperature it needs to be. Occasionally it drops lower on a rare day we have had rain and colder temperature. On these days I have just used by low wattage under aquarium heater which has got it back up.
Since the heaters, both work and it is just the thermostats that seem inaccurate I might get one of those external temperature controllers that have a probe that goes into the water so it will turn them on and off depending on the water temperature.
I wonder if newer heaters are more accurate today?