An idle pool in the winter time can be a corrosive pool
Many pools are seasonal and we know better than to drain them so that the plaster does not dry out. But did you know that cold water is corrosive water? Utilizing your Ryznar Index Calculator, factor in a pool temperature of 60° and you will soon find out, with all the other parameters the same, you may have a corrosive water condition on your hands.
What to do: It may be as simple as adjusting your controller pH setpoint to a higher value or manually adjusting some of your other chemical values. Whatever best meets your site conditions, just don’t ignore it!