Please check me on this. I bought the CYA 50ppm Standard solution from TFTestKits to verify my testing procedures. The way I understand it, I use this solution in place of pool water, mixed 50-50 with the CYA reagent, (just as I would with pool water.) Mix it up, and let is sit for 30 seconds. Mix again, and pour into the view tube. In direct sunlight, with my back to the sun and the view tube held at waist level, I should get a reading of 50, correct?
The reason I ask is that to my eye, the dot disappears at 70, instead of at 50. The way I've been reading my test, my CYA must be 20ppm lower than I thought it was. I started the season with a CYA of 40 (by my reading) which I thought was extremely low since my reading last winter was 70, and I only replaced about 15-20% of the water. I later added enough CYA that I should have reached 80, but it never got there. I have been operating under the assumption that my CYA is 70, but based on this test, it must be closer to 50 or 55.
Note that if I do it the same way, but facing the sun, I get a reading of 60 instead of 70, but still not 50.
Anyone have any guidance or advice on why this seems to read high to me?
[Edited because I had written "50%" instead of "50ppm" - It's only a factor of 10,000! ]