A couple of freezing nights coming up - keep the pool running or drain?

[FernTheBrute]

I try to close my pool as late as possible in the season to make its reopening easier by having cleaner water in the spring. It seems everyone around here (Québec city) has already closed its pool in the last few weekends, which seems premature since we got 20c today and will get a couple of days above 15c next week. Thr normal is around 8-10c in the day.

However, we'll get a few freezing nights this weekend (forecast around - 3). Is there any possible issue at that temperature if I keep the pump running 24/7?

 

[sande005]

No worries - keep your pump running at least during the coldest parts. It's all about the water temp. If the pool water is warmer it will warm whatever it flows through, and therefore no risk of freezing. If it wasn't moving, smaller amounts could cool down to the below freezing air temp and then you'd get ice. Or, if the differential was much greater, then it would become a concern. But if your pool is even at 7, there is an awful lot of water to cool down during the cold parts of the night. But time to anticipate closing on the next semi-nice day...

 

[JJ_Tex]

I'm in a much different climate, but we do not close our pools and get down to the 20's (~ -5c) multiple nights per season. Just keep the water moving through the equipment and you will be fine. Make sure you have a plan to drain water from the equipment in the event of power loss or equipment failure as those will freeze and damage much quicker than your actual pool.

 

[FernTheBrute]

No worries - keep your pump running at least during the coldest parts. It's all about the water temp. If the pool water is warmer it will warm whatever it flows through, and therefore no risk of freezing. If it wasn't moving, smaller amounts could cool down to the below freezing air temp and then you'd get ice. Or, if the differential was much greater, then it would become a concern. But if your pool is even at 7, there is an awful lot of water to cool down during the cold parts of the night. But time to anticipate closing on the next semi-nice day...

The weather forecast changed a lot, which messed up my plan of lowering my chlorine level a bit before adding polyquat 60 24h prior to closing.

Outdoor temp won't rise above 4c for the next two days and will drop to -5c both nights/mornings, with wind chill of -10 at night and 2c during the day. So in the next 48 hours, it will be 50/50 above and below freezing and always under my current temperature. Is there any chance my 6c water could drop below 0c in that interval? Should I run my pump on low instead of high at night to prevent to much stirring / cooling of the pool?

The temp will rise back up above 15c for a couple of days after that (we have a truly messed up fall season) with some rainstorms.

 

[sande005]

It would help a bit to cover the pool and/or equipment to keep heat in. I very much doubt you'll have much issue with two 12 hr periods below temp. But you are flirting with the weather! If you are in Saguenay the snow could push your water temp down pretty quickly. But, this will not be a damaging freeze even if you do get snow and some ice formation. Fast or slow, just keep the water moving. But nothing will be cold enough long enough for damage. Worst is you'll see ice on any standing water on the equipment pad or the area around the pool.
I've had up to 2" of snow falling into my pool before closing/after opening. It can be very pretty! Nerve wracking, but pretty!
But plan for closing really soon, no matter how disagreeable it may be to work in the cold with everything wet from rain.

 

[ajw22]

To understand when you need to worry about the pool or equipment freezing read The Physics of Freezing and Freeze Protection.

 

[FernTheBrute]

It would help a bit to cover the pool and/or equipment to keep heat in. I very much doubt you'll have much issue with two 12 hr periods below temp. But you are flirting with the weather! If you are in Saguenay the snow could push your water temp down pretty quickly. But, this will not be a damaging freeze even if you do get snow and some ice formation. Fast or slow, just keep the water moving. But nothing will be cold enough long enough for damage. Worst is you'll see ice on any standing water on the equipment pad or the area around the pool.
I've had up to 2" of snow falling into my pool before closing/after opening. It can be very pretty! Nerve wracking, but pretty!
But plan for closing really soon, no matter how disagreeable it may be to work in the cold with everything wet from rain.

I'm in Quebec city. I'll monitor my water temperature until tomorrow, but I'll probably close next Saturday