There have been more than a couple of posts in the last few years regarding similar results with the standard solution which suggests that the standard may not be bad. Compare your results. Here's a couple threads with photos of results with the standard solution:
I ordered a set of standard solutions from tftestkits on Aug 17th, and just today got around to trying out the 50ppm CYA solution, to make sure I'm testing my new pool accurately. I dissolved enough CYA granules in my pool to achieve 20ppm (38oz for my 14,060 gal pool), and when I test the...
The 50 is 60. Great to know. Maybe I’ll email them and let them know. I just pretend I have 30. I can also read the bottom line of an eye exam chart. That’s my down fall. Actually the 50 is 40. I changed my post on that.