Quote Originally Posted by BigDave View Post
CYA doesn't settle, you usually lose it by splashout or backwash. A drop of 65 to 50 may just be the accuracy of the test.
In other words, by dilution. But try to always run the CYA test the same way. One trick I use is to pour it back into the squeeze bottle and run it again (it doesn't change the solution to do this). Sometimes I do it three times, always trying to do it the same way. This helps me neutralize errors in any one of the readings, and I'm not using any more reagent, just reusing the sample.