I'm all for preventative here- but make sure the ingredients has poly...anything 60%, or don't use it at all. I just purchased some called Pooltrine from Lesliespool.com for $7.73/qt- CHEAP! Granted there's a small handling charge - but it stores and keeps well. Read the label, though- must say poly... 60%! I use it once a week - just a small maintenance dose- small price for assurance.