I like the Ca and Mg tests but the Alk just doesn't work very well....at least the batch of reagent that I got. I contacted them and they sent me a new bottle but is was the same lot and exp date and tested the same. I contacted them again and asked for another one but a different lot to see if it is the reagent. Supposedly they are sending me another one and I will compare. The colors are so light that it is hard to tell when to stop adding drops.