Calcium Hardness TF-100 Test Seems Inaccurate

[floridarandy]

Just received TF-100 kit and ran through the tests. Everything was as expected except Calcium Hardness. The instructions state 10ml of pool water...10 drops of r-0010 and 3 of R-0011L...followed by R-0012 in drops x 25 to get final reading. By this method 35 drops of R-0012 were required which would indicate Calcium Hardness of 875! I re-ran the test with the same result.

A Hach AquaChek 7 test strip indicated a more normal 250 (approx) and a quick trip to PP tested 350.

We've had this pool for nearly 20 years and CH has never been 875.

Any idea what could cause this test to be so far out of "norm"?

I note several other posts of strange CH readings with TF-100.

Thanks

Randy

 

[PoolBrews]

Just an FYI... I found that if I wait 30 seconds after putting in the R-0010 to put in the R-0011, then wait 1 second between each drop on the R-0012 I get much more consistent and reliable numbers (i.e. they match fairly closely to a local store that does a drop test).

I was getting numbers 100-200 higher when not waiting for 30 seconds after R-0010.

 

[mknauss]

A SpeedStir helps tremendously in getting accurate CH readings, especially higher amounts. I get up to 1000 ppm CH in our pool and the testing is consistent with what it should be based on water additions throughout the summer.

I would not compare a drop based test to a test strip ever.

 

[PoolBrews]

I agree with the use of a speed stir - I wouldn't test without it!

 

[floridarandy]

Rebecca at TFT suggested that when new the R-0012 dropper delivers a smaller than desired drop. She suggested wiping the dropper end between drops. I also invested in a speed stir. Both suggestions resulted in a drop in CH from 875 to 450. I suspect it will drop further as the dropper "breaks in". I must say that in nearly 20 years of pool testing this is the first time this phenomenon occurred.