Just got my brand new air water ice rodi it's reading 0 tds but when I test the po4 I'm getting a reading of 0.1 with red sea test kit same reading I'm getting with tap water
Gonna buy new test kit but I'm getting fed up
Matt, all these hobbyist grade phosphate test kits are weak tests. None of them are truly reliable. They'll get a reading that might be close, but nothing to hang your hat on. As already stated by Jarrett the Hanna Photometer is your most affordable way to test for phosphates.
If you call Hanna and ask them about there checkers they will tell you themselves that there Phosphorus Ultra Low Range checker is more accurate then there phosphate checker and they recommend it. They have great customer service you should call them and tell them what you are trying to do they will point you in the right direction. I also have one of these test kits if you give Jarrett some water I will also test it when I see him in august.