The first several times I did my CYA test I filled the mixer bottle to the arrows on the label, which should have given me a 50/50 mix. I was getting about 50 on my CYA readings pretty consistently. Out of curiosity one day I decided to figure out how much of each (water & CYA reagent) was in the mixer bottle. Come to find out the arrows on the label were off and I was getting more reagent than water. The past 2 times I've done my CYA test I measured both the water and the reagent in my test tube before pouring them into the mixer bottle. Both of these past 2 times I've gotten a reading of 30. I know there's not really much difference between the chlorine requirments for a CYA reading of 30 or 50, but I just thought I'd let you all know that you might want to check to see if filling your bottle to the "arrows" was really a 50/50 mix for you.