I've got an in-ground pool, and a DE filter from Jandy. The pressure gauge is in an assembly bolted to the top. The assembly looks like something like this (image from catalog, mine is pretty much ...
I have jimmied up a pool heater from an idea on YouTube, but just expanded it. I have a water line of 2" PVC, piped down to 1/2" copper, so it can run through a coil, then increased back to 2" PVC, ...