Ph drops over winter. Why?

Saturn94

Well-known member
Mar 11, 2015
711
Virginia
I’ve noticed every spring at opening ph has dropped from about 7.5 at closing (October) to about 7.0 at opening (May). Any idea why? At opening, I’ll bump up pH back to about 7.5 and it stays there all season; never have to add acid.

The pool stays covered all winter; no chems added. It’s covered by a solid tarp over a mesh safety cover.

There are a lot of dead bugs and in there at opening. Could their dead bodies be driving pH down?

It’s not really a problem, but I’ve always wondered what is going on here.
 

Divin Dave

TFP Expert
LifeTime Supporter
Oct 2, 2013
5,638
Longview, Texas
The same thing happens to me. 3 weeks ago when i started balaning it out, my pH was 6.9
Generally during the season, it hangs out at around 7.4 and is stable all season long.

I dont have any evidence and I havent done any sort of testing to back up what Im going to say, but it seems logical to me.

Rain seems to be a good candidate for lowering the pH. Rain is acidic. According to google, the pH of it on average about 5.6. During winter and early spring in my part of Texas, we get a good bit of it so thats what I chalk my pH drop up to.

I just raise it back up in early spring and go on about my business until the next year.

Maybe someone else will chime in with more scientific reason for it than what I have.
 

Saturn94

Well-known member
Mar 11, 2015
711
Virginia
The same thing happens to me. 3 weeks ago when i started balaning it out, my pH was 6.9
Generally during the season, it hangs out at around 7.4 and is stable all season long.

I dont have any evidence and I havent done any sort of testing to back up what Im going to say, but it seems logical to me.

Rain seems to be a good candidate for lowering the pH. Rain is acidic. According to google, the pH of it on average about 5.6. During winter and early spring in my part of Texas, we get a good bit of it so thats what I chalk my pH drop up to.

I just raise it back up in early spring and go on about my business until the next year.

Maybe someone else will chime in with more scientific reason for it than what I have.
Sounds like a reasonable explanation. The tarp I use does leak some, so rainwater does get into the pool over our typically wet winters. Maybe one day I’ll take a rainwater sample and test it (suppose to rain all day tomorrow).
 

borjis

LifeTime Supporter
Aug 19, 2014
3,048
Pacific NW
I know mine (uncovered and at fill level over winter each year) has the ph go down every winter too.
Not very far down, but not staying at 7.5 that it was when closing.
Lots of rain fill and draining the excess fill over that time. I think it is the rain.
 

Divin Dave

TFP Expert
LifeTime Supporter
Oct 2, 2013
5,638
Longview, Texas
I never have to add water due to evaporation probably from about mid-October until maybe mid-May. It doesn't evaporate enough until the rain fills it to the brim.

But in the summer, I have to add a couple or more hundred gallons every week due to evaporation and the pH in my fill water is 7.4

I guess what Im saying is I don't believe the pH drop due to rain is a quick thing, as least for me.
I think It's something that happens over a period of time by dilution.