Different reading with different test kits

[kira76]

Hi guys, recently I got my hands on the Hanna Calcium test kit. Just tested it and it gives me a reading of Ca - 520. All along I've been using the Salifert Ca test kits which gives me a reading of 430ppm.. Understanding that the Salifert test kits requires me to count drops and see colour change while the Hanna test kit is digital. But the difference seems too big. Now I'm totally confuse as to which test kit to trust?

Btw. I used the Hanna test kit twice, first reading, 533ppm. Second reading, 520ppm. My Salifert test kit almost always give me a range of 410~450 ppm.

[comycus]

check expiry date of Salifert Ca and how long have you been using the current set?

have you callibrated the Hanna checker?

suggest testing on quality pre-mixed SW @ recommended temperature where manufacturer has given set parameters to give you a clearer idea which tester is accurate.

[kira76]

I think I got check Salifert Ca expiry date before and it should be sometime in 2014. Hanna checker Procedures itself already calls for a callibrated of the checker with RO/DI water.

I think the question now is which is more accurate in terms of the method in which the test kit gets the results. Salifert itself need me to determent when the co our change while Hanna checker uses digital spectrometer(I think).

Maybe I'll test the Hanna checker with the test sample from Salifert.