I use a Hanna for phosphates and api for CA and Alk. I use the Hanna because I cannot tell the color differences when doing the phosphate tests, so the digital read of the hanna is nice. People don't like the API test kits, but they are cheap and work. For CA, it isn't critical and an acceptable range is huge. For alk, you want it accurate, but it isn't a complicated test. I want the test to be quick and easy; otherwise, I won't do it. To protect against errors, I usually buy a new test and check it with the old test just to see if they are the same. And they have always been the same...