Why cold water is the trigger
The best closing signal isn't a date — it's water that holds below about 60°F. Algae is nearly dormant there, so a pool balanced and covered in cold water emerges in spring looking much like it went in. Close warm, and the cover becomes a greenhouse: weeks of algae growth with no sanitizer, paid for in shock and scrubbing at opening. Swimming may end in early fall; the close itself should wait.
Closing day, in order
Balance the water first — pH slightly high-normal, alkalinity and calcium in range (the saturation-index calculator shows where you stand), then a final shock a few days before the cover goes on. In freeze country, blow out and plug the lines and drop the water level per your pool type; in milder climates, many owners just run the pump on freeze protection. Label honestly: the details vary by pool construction — follow your equipment manuals over any generic checklist, ours included.
Frequently asked questions
When should I close my pool in Michigan?
Typical closings across Michigan run Aug 21 to Sep 15, as daily averages fall back through the low 60s°F. The best single trigger: close once water holds below about 60°F — cold enough that algae has gone dormant, so the pool winters clean.
Is it bad to close the pool early in Michigan?
Yes, early closing is the classic mistake. Sealing a still-warm pool under a cover hands it to algae for weeks. Hold on until water is reliably below ~60°F, even if swimming ended a month before — a late close is what makes the spring opening easy.
Why do the dates differ across Michigan?
Because each city's dates come from its own NOAA 1991–2020 station records, and geography does the rest — elevation, latitude, coastlines, and urban heat spread the same milestone across weeks. That local spread is exactly what a national "open on Memorial Day" rule misses.