I recently just bought a home in Glendale, AZ that has a Shasta pool. I've been trying to figure out all the valves in my filter system and I have them all figured out except for a valve that is labeled Vision. It is on the outlet side of my filter and the valve leads into a pipe that does a loop through a white upside down canister back to the outlet pipe. I searched online and through this forum but I didn't find anything about it. Could someone inform me what this is for? Thanks.