A little tip! After you mix your hanna po4 checker powder, set it for 3 mins as usual, then when it reads the result take the sample out, open it and clean the inside of the vial with a q-tip getting off all dust and microbubbles. Use the other vial to make the test again. Then put your sample in and have it read it instantly (dont do 3 mins this time). The results will be lower if your vial had bubbles or dust stuck to it.
My reults whent from .24ppm to .11ppm!
My reults whent from .24ppm to .11ppm!