I think this would be a cool project if you could provide suggested modules to attach to the Raspberry Pi + OSPi. I know I would be interested in this but I know nothing about the various hardware used to accomplish what you are suggesting nor do I know how I would hook them up.
Is this something that would make managing a pool easier? Or just a way to give you extra information? If so, how?
I think if you can find a way to make some instructions and get the hardware working properly I would be open to making a mobile front-end for it.