I test my CYA around twice a month. On 7/7 and 8/6 my CYA was at 60. I tested it today and it was at 40.
When I test my CYA I look at the cylinder, in sunlight at waist level and I have my wife do the same. This gives the test a little more validity in my opinion.
I live in Phoenix and we have not had that much rain recently. What would explain the drop of 20 points in just over two weeks?
I decided to throw a few chlorine tabs in my floater as well to elevate my CYA back to ~60.