Which test to trust on CYA

[chem geek]

I had a similar discrepency come up when measuring Calcium Hardness (CH). The pool store said I had 350 while my Taylor K-2005 test kit said I had 250. I got another fresh batch of chemicals from Taylor just to be sure and got the same results. I also tested my tap water and got the same results as my water company published (though had to do some conversions of the units and magnesium/calcium ratios). I've never trusted the pool store since.

For the CYA test, remember that the appearance of the black dot has to completely go away. There is a thread I saw on this forum that I can't find anymore that discusses some of this along with some photos. Since the SWG system is at its highest efficiency when the CYA is at 60-80, you should see that you can lower your power level and/or percent on-time to get the same chlorine level (FC) at the higher CYA.

Richard