It is not imperative that you add polyquat when you close. Some people don't. I don't think Al (Poconos) does, but I may be wrong about that. It is just some added insurance against something getting started in your water. Where I live (WV), it isn't unusual to have crazy temp swings in the winter. We frequently will have days with temps in the 70s in the middle of the winter. If I lived someplace where it stayed freezing cold all winter long and my pool pretty much stayed a solid block of ice, I wouldn't be quite as concerned about adding it. But, since I may have temps in the 20s one week and then the 60s or 70s the next, I use it. It certainly doesn't hurt. Whatever I'm doing is working for me. I have never opened to anything but clear water. (Knock on wood!!)