Red Sea Phosphate Test Kit - Detecting Zero

[SPSReeferMI]

Hello,

I'm using a red sea test phosphate pro kit and I suspect that these may not be that accurate for very low values, but I'm looking for it to tell me that I'm close to 0.05 ppm. Ideally, it would be able to read phosphate values of .04 through .10 without a problem. Presently, I'm using a Reefbot to test phosphate and using Red Sea's Phosphate Pro test kit to do so. I did test phosphate manually using Red Sea (showed zero) and Hanna ULR (showing 29ppb or .09). Has anyone been able to use Red Sea consistently? I sort of suspected that it would struggle below .03, but I was surprised that it struggles at .09.

Thanks for your help!