If you want a simple, low cost, quick solution to building a aquarium temperature probe, I would probably not use a Raspberry Pi. Instead, you can use a much lower cost ESP8266 microcontroller + a waterproof DS19B20 temperature probe. Once you have these wired up, you then have to decide whether you want to directly integrate with Hubitat or Home Assistant. If Hubitat, then you can use HubDuino to easily configure the ESP8266 and integrate it with your HE hub. If Home Assistant, then use ESPHome to very easily integrate with your HA hub. Both solutions can use the exact same hardware, so it is a very flexible solution.
In either case, there are HE to HA , as well as HA to HE integrations available to move the data between the two systems if necessary.
