pH balancing in winter (low temperature)

iflyjetzzz

Well-known member
Jun 16, 2011
57
Las Vegas, NV
#1
I have a new pool, completed in August. The current water temperature is now starting to warm a bit but is still in the (high) 40s. It has gotten as low as the high 30s this winter here in Las Vegas.
The pool is a salt water pool and I occasionally use the spa portion of the pool. This allows me to run the salt cell when the spa water heats up. This has easily taken care of chlorination in the entire pool, as the spa water mixes with the rest of the pool water daily and chlorine demand is low with the low temperatures.

Here is my question/comment. When testing the pH, I've found that it reads low when the temperature is in the 40s (say 7.0 for example) and rises considerably (say 7.8) when the sample is warmed to room temperature. I've found that this has occurred every single time I've let the sample rise to room temperature. So, should I try to make my pH correct for the pool temperature or for room temperature? So far, I've been trying to keep the room temperature pH closer to 7.2, as I have a new plaster pool that is still using a considerable amount of muriatic acid.

Interestingly, I looked online for how pH is effected by temperature. I was shocked to see that more than a few academic chemists state that pH falls with higher temperatures, while others state that pH rises with higher temperatures.

TFP community, is this something that you check for? How do you handle pH during winter?
 

AUSpool

Bronze Supporter
LifeTime Supporter
TFP Guide
Sep 23, 2015
458
Sunshine Coast, Australia.
#2
What is your TA at? I don’t think its your temp warming up but out gassing of CO2. With your auto cover on your water will not off gas as much as it could and your accumulating CO2 which will lower the pH. When the water sample is allowed to warm and out gas the pH will rise accordingly.
 

iflyjetzzz

Well-known member
Jun 16, 2011
57
Las Vegas, NV
#3
Like I stated, around 7.0 when I test it cold. About 7.8 when I test it at room temp.
Perhaps just outgassing - I'll check it with one sample sitting outside for a while and one sample warmed to room temp.

I hadn't considered that; good point.
 

AUSpool

Bronze Supporter
LifeTime Supporter
TFP Guide
Sep 23, 2015
458
Sunshine Coast, Australia.
#4
I was asking about your total alkalinity, TA, but a list of your complete current test results would be very helpful. Some SWG shut down when the temps drop, check on this too. When the temps drop in winter everything slows down so there’s normall not to much to worry about, just keep an eye on your CYA and in particular your FC. You don’t want to end up in slam territory due to running low on chlorine.