The red sea alk pro was far better then I imagined!
I Just got the Hanna checker for alk, ordered refill for my half full red sea alk pro kit that expired in 2015 while I was at it. The red sea alk test that is in my expired marine care test kit (2016) is off by miles (ranging from 10-12dkh from same sampled water), but both the expired alk pro (8,5dkh) and the new refill (8,5dkh) gives me about same results as the Hanna checker (153 ppm/ 8,568dkh). Cool thing about the checker is that it gives me readings in ppm, and the guess work about when the color changes is eliminated. About 12 USD more for the checker then the alk pro, and refills are about 33% more expensive for the checker then the alk pro per test (I never squirt back into the bottle). The expired magnesium pro and calcium (2015) from red sea gives me also the same results as the new refills (2021).