Each year I seem to have a metals issue in the water. Because I have to shock my pool when I open it, I was planning to start it up a few days before pulling the cover and putting Pro Teams Metal Magic (which I used last year) under the cover so I can shock it when I do pull the cover. The problem is that the directions for the Metal Magic says to use with pool water over 60 degrees and my water will be about 53-55 under the cover. Any suggestions?