I would be curious how the CYA was tested. Most pool stores, at least in my area, use the plastic cylinder with the plastic graduated spoon that slides up and down and has the black dot in the bottom. The accuracy falls off at about 100 or so. After that, one pool store worker admitted that they just guess. I have learned never to trust one pool store. I get multiple samples and multiple readings. The only down fall is now trying to figure out who to believe. So the more I read on this Forum, You almost have to learn and do your own tesing.