The heck is this thing?

Hey all, I'm opening my pool for the first time myself and it's going pretty good, I think, but I have a device that's leaking and it's the only piece of equipment that I am unfamiliar with. The pool company that installed our pool and that has done all of our openings and closings hasn't mentioned it, that I recall, and I've never asked about it. Now it's leaking like a sieve and I can't even search online to find out why because in all of my searching I can't identify it or know what it's called or what function it serves. It's a clear tube that appears to contain sand and there's a ground wire connected to it. I don't even see it in any photos of other peoples' pool equipment!