Why is my PH Dropping?

[poolneophyte]

I have a SWG but my PH is dropping. My current TF100 test results are:

PH = 7.2
FC = 13
CC = 0
TC =13
Borates = 50 (approx.)
TA = 70
CYA = 80
CH = 50
Temp = 85

So far this season, I have added 6 pounds of 20 Mule Team Borax to raise the PH. I have recently added CYA to bring it up to my target of 80. It has only been a couple of days since I added the CYA so I am still trying to dial-in on the correct setting for my SWG. That's why the FC is presently on the high side. I want to target a FC of 8 or 9.

I have read the extended test kit directions for the PH test and understand that the reagent is compensated up to a FC level of 10. When FC level is between 10 and 20, the test result is higher than actual. So, if I understand this correctly, I may have a PH of less than the 7.2 reading that I got today.

Since SWG's tend to cause PH to rise over time, I'm not sure why mine is dropping. The only thing different this year is that I am using a solar blanket. Could this have an effect of the PH? Also, since my borate level is already around 50, should I still use more borax to raise the PH?

 

[JasonLion]

Continuing to use borax to raise the PH is fine.

The solar blanket will stop CO2 outgassing, thus preventing the usual PH rise. Also, your TA isn't all that high, so I wouldn't expect all that much PH increase, though seeing a little would be normal without a solar cover.

Remember that adding CYA will bring down the PH.

 

[poolneophyte]

I didn't realize the effect of adding CYA on PH. I went back to the Pool Calculator and found that adding 50 oz of stabilizer will drop the PH by 0.39 which is pretty much what happened. Thanks again for the help.

 

[poolneophyte]

Follow-up question - Should I even bother with adding borax now or just let the PH rise on its own over time?

 

[JasonLion]

As long as your PH is at least 7.2, you can just leave it alone and it will most likely come up on it's own over time.