I've got a Taylor K2005 DPD test kit that I'm using to test my water.
Recently a new store opened up in town, that's using the Waterlink Spin Labs, so I gave them a try. Their Waterlink Spin Lab hardness is consistently 70-100 ppm higher than what both I and Leslies get with the Taylor kits/regents.
Today I ran a "controlled" test. I took 4 samples at the same time from the same place in my pool, in 4 samples bottles. I took one to Leslies, took 2 to two different stores using the Waterlink Spin Lab, and measured the 4th myself -- all tested within a hour of taking the 4 samples.
The 1st Waterlink Spin Lab measured 193 ppm.
The 2nd Waterlink Spin Lab measured 205 ppm -- within the tolerance of the measurment.
Leslies measured 110 ppm.
I meausred 105 ppm.
So whose is right -- me & Leslies? Or Waterlink Spin Lab?