I started with the Salifert test kit and could not read the colors at very low levels (which is typically where you want your phosphates). It always looked to be reading zero to me when it was probably more in the 0.03-0.05 range. I've since switched to the Hanna ULR Phosphate checker and I'm happy with the results. The powder packets are a bit annoying and I feel they could package them in a way that's easier to use, but once you figure them out it's not difficult. I'd highly recommend picking one up.