ULR is for <1 ppm (ULR Phosphorus .6 ppm Phosphate max or ULR Phosphate Checker .9 ppm Phosphate max). If you keep phosphates higher than that, then don't go with ULR. If I have phosphate problem and ULR isn't high enough to read, I will go with simpler-cheaper Salifert tests until back where I want.