I have been using the Hannah hi713 for several months and was always getting a reading of 0.00 ppm. I also had issues with color fading on sps but just to make sure before I started dosing phosphates I purchased a Hannah ulr phosphorous checker. My first test came up 3ppb or .009 ppm. So I proceeded to dose 1 ml of neophos in my 100 gallon tank. I tested the next day same time and got 19ppb (.058 ppm) I then tested again as this didn't seem right to me and got 4ppb (.012 ppm) which seemed in line with what I dosed. However I decided to do one more test to make sure and I got a reading of 15 ppb (.045 ppm).
Which number should I be going off of? Did I possibly get some detritus in the vial on the higher readings?
Which number should I be going off of? Did I possibly get some detritus in the vial on the higher readings?