I will throw in my vote for Salifert calcium. In my experience just as accurate as Elos but a little easier to use. I also have a salifert alk test which i picked up to verify the API kit i was using (it did). I like the salifert alk kit but i haven't had a chance to verify it against another higher end kit. I'm currently using a seachem mag kit which i would not recommend. It's a PITA and was out by about 15% against its reference sample. I've come up with a factor to correct for the kit's error so i keep using it but will not buy again. I've also got salifert phosphate, nitrite, ammonia and silica kits as well as API nitrate kit and have no problems with them, but i have not verified those kits against anything so i can't speak for their accuracy.
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