As to closing a pool, at least where the water temp drops below freezing.

Provided you use a solid cover that blocks the light, little or no algae should grow even at higher temps during fall. And any algae still alive should be killed over the winter by the low tempertures?

Seems to me that if you put a winter cover a green algae pool, that algae should die over the Winter due to low temp and lack of light and you should find a clear pool with the bottom covered with dead algae come Spring.

That seems logical to me, but does it hold true?
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