Ok, experts, I got a new Spa in July. I have city water. Pool store added metal out on initial fill, saying I needed it, and will require it with each fill, as "you never know if there are metals in your city water". About to change my water, and need to know if I really need it, or if pool store is really just wanting my [emoji383]. Don't want to do the wrong thing and not add it if needed, but don't want to add stuff I don't need. Thanks for your help