Based on new (haven't been on the shelf for over 1 year), I found that both Hagen and Salifert gave me results for calcium that were within 10ppm of each other, so I have to believe they're fairly accurate. The big thing I think that Salifert has going for them over Hagen is ease of use. Hagen is 1 drop, put the cap on the test tube, shake, repeat. not so much fun when 1 drop increases sensitivity of the reaction in 20ppm, for calcium of 400ppm, you're looking at 20 drops.