How cold does it get there? And how long does it stay cold? If your water is below 60 deg, or, better, below 50 or even freezing during most or all of your closed season, shocking before you close should be enough.

I'm in NJ and once I close my pool I peek under the cover about once a month and usually, there's nothing to see. The water will either be clear or frozen, and that's fine. If you have ice on top of the water, algae's probably not growing underneath the ice. Too cold.