I had the same suspicion, so I had tested it with 4 different tests. Two different drop kits from HTH, 1 strip from HTH, and 1 strip from Leslie's pools.

All give the same results. I forgot the exact reading of the CYA, but I tested it multiple times and it was always at the perfect level.

Also, after adding 1 gallon of bleach and testing 3-4 hours later, the tests showed it at 2 ppm, so the test kits are working.

Thanks!