Wait, Are you talking about the phosphorus one? Because I see a Phosphate high, Phosphate low and Phosphorus one.... I have low range Phosphate.. Maybe its broken? It has been 0.00 since inception of the tank. I have been running GFO since day 1.
Ok, yeah that one reads a little bit wider range, so it's likely not true zero. Even the ULR measures into a range of values of +/- depending on the reading you get. I own both. They're fairly accurate for what we use them for, but you don't want to get too caught up with chasing numbers. Some of the most successful SPS keepers on these forums run phos levels that would make your eyes pop. At the end of the day, it's all in how the tank is looking to you.