Calcium testing from two pool stores varies extremely from my tests.

[djbigelow]

I tested my calcium with the TF-100 kit, and they say to multiply the drop counts by 25.
First test 475. Dropped pool about 8-10 inches at a time and refilled - 6 times with fresh water.
Should have but don't have home test results for that.
Pool store said calcium at 140.
Added 10 lbs calcium chloride
Home test said 525 on June 29, 2016.
July 1, 2016, two pool stores say 200 - 225. And I notice they are multiplying drop counts by 10. Both are using Taylor reagents 10, 11, and 12. (I'm assuming there is only an 11L, that is used for the calcium test and if not, that could be a big variable).
Home test July 3, 2016, calcium at 425.

Can anyone help me understand why the variance in the multiplier and any other factors I may be missing?

 

[oldguy70]

Are you using 10mL or 25mL of pool water?

 

[Texas Splash]

First thing I would ask you .... are you also using a "speed stir"? That has been known to make s difference with the CH testing. Also remember with the CH test you have two options:

10 ML testing (standard method):
- Use 10 drops of R-0010 (swirl), then 3 drops of R-0011 (swirl), count number of R-0012 drops and multiply by 25.
25 ML testing (used for low CH or precise testing):
- Use 20 drops of R-0010 (swirl), 5 drops of R-0011 (swirl), count number of R-0012 drops and multiply by 10.

Regardless, I would stick with your TF-100. As long as you are following those testing instructions (for ANY test) you are more inclined to be accurate than any of the stores. Comparing your results with theirs will only leave you confused and frustrated trying to find a middle-ground. Also remember, even if your CH is slightly elevated (~ 400 is low for many places), you can compensate with the lower pH and TA to maintain the proper CSI reading for the health of your plaster. Just some FYI if you didn't' already know about that.

 

[duraleigh]

Trust your own testing. We cannot confirm why pool store testing is so lousy but it is.

Test and dose carefully and please stay out of the pool store.