YeahThe stated accuracy for that checker is +\- 5ppb +5%. So for a reading of 30 ppb your sample should actually be within the range of 23.5-36.5. So getting multiple tests that are within 4ppb is completely within margin of error.
So were the tests done with a reading of 200ppb tested from water from the same tank? I guess that’s the part that I’m confused about. I originally thought you tested your tank and got a reading of 30 with one batch of reagents and got a reading of 200 for the same tank from the other batch or reagents.
i tested water 3 times with old reagent, 200ppb all 3 times. I retested with new agent with the same procedure and got acceptable results ~30ppb 3 times.
Original question was whether reagents had external factors that could affect reliability and the likelihood that I had reagents that were “wack or bad” even though they were within the exp date.
I have compared Phosphorus naming on packets to checker, to make sure it’s phosphorus and not phosphate but no confirmed number yet I am out of town til Friday