As a member of the lightning-bolt.net team, I have a passion for coding and hardware. It made perfect sense for me to attempt to combine this with my love of the Pond.
So we set about writing a temperature reporting system that saves the values in a database, with set sms triggers on low and high thresholds. There are many guides regarding the hardware https://www.instructables.com/id/How-to-Build-a-Raspberry-Pi-Temperature-Monitor/ for eg.
The biggest hurdle has been the probes, With 4 Air Temp, Top, Middle and Bottom of the pond. None of the probes I have purchased have remained waterproof for longer than 7 days to date.