I use their phosphate and alkalinity. I've heard in the past that the calcium one isn't as accurate, so I use the red sea pro for that. The accuracy on it might be better now, but I'm totally happy with the red sea pro kit, and will keep using that. The checkers are very easy to use, and I find them reliable. One trick that I've learned is to keep any handprints, etc. off the outside of the tube, otherwise the reading will be off. I always hold the tube with a towel to keep it clean.