Reef-Pi works with DS18B20 1-wire digital temperature probes. There are a lot of probes, but they're a crap-shoot how well they work especially at the common import pricing. Most of the sensor ICs contained in these probes are fake:
How to tell original from fake DS18B20 temperature sensors. - cpetrich/counterfeit_DS18B20
github.com
Previously, the "Drok" probes from Amazon (with the 10ft red silicone jacket) were the go to probes,; they used good steel caps (some sensors were not at all stainless steel), good quality cables, and real sensor ICs.
I wanted to do some value add screening on sensors since a lot of people had problems with sensors in general, so I bought a new lot of Drok probes from Amazon (20 or so) and... ended up having Drok cables with fake sensors AND with out of spec temperature performance (1C out with self-heating). (See:
https://www.reef2reef.com/threads/r...controller-boards.499890/page-34#post-7998672 )
Most people use the fake sensors as its all there is available, and most actually do actually work, but you may have to try a few to sort out ones which are good in your setup yourself, and verify the temperature performance is correct (which you shouldn't have to do, but here we are). I want to make some better probes with actual Maxim chips, but its going to take a bit longer to qualify them. I'd subscribe to the thread if you're interested.