pH Test Interpretation Please

[mcolflesh]

Hello,

Here are my test results from this evening after concluding a SLAM (passed OCLT this morning):

FC: 8.5
CC: 0
pH: 7 (I think)
CH: 100
TA: 80
CYA: 60

pH test result I interpret as 7:


I added 5lbs. of soda ash per the pool calculator (mixed it as a slurry and poured into pool in several places with pump on recirculate). Test results after an hour or more:


Did I overshoot?

 

[JohnT]

Looks like 8.2 to me.

 

[Richard320]

Yes, you overshot. I see that first test as 7.2 or maybe 7.3. Concentrate on the shade, not the intensity. I like a white background and holding it at arm's length and squinting so it's blurry.

The problem with pH is that it is logarithmic and TA also affects the dose. It's not as simple as if 4 ounces raises it from 7.2 to 7.3, 8 ounces will get to 7. 4, 12 ounces to 7.5 and so on. The same holds when adding acid, so be sure to do a careful TA test when figuring out acid to get it back down a little. Rule out any interference by wiping the tip of the R-009 with a damp paper towel before you do the TA test. And when you lower pH, aim for 7.5 or 7.6. Better to undershoot and repeat than overshoot and end up on a see-saw.