I use Hanna for KH and PO4, and Salifert for CA, nitrate, and MG. You will probably receive many suggestions on which tests are the best. Ultimately, it also depends on your personal preference for test handling and which one you are most comfortable with. There are many controversial opinions about the Hanna checkers, but I am generally very satisfied with mine. One weakness of the Alkalinity checker is that it consistently measures the KH about 0.6 too high compared to the reference (several ICP cross-checks). As long as it’s always 0.6, I don’t mind, and that’s the case. My Hanna Phosphorus 736 is now at least 15 years old and still works. It is rare for an electronic device to last this long. The key to using it properly is working very cleanly and following the manufacturer's instructions. Even when compared to the ICP tests I have done, the checker is very accurate (with a deviation of +/- 10% to 15%). I can reproduce the measurements with several test runs, which is another plus. I don’t think there are many tests in the hobby that are really much better. The problem with the Salifert nitrate test is that it cannot be read very accurately in the lower range. I have been planning to buy a better test for some time, but so far I haven’t been able to part with Salifert because it’s just very easy to use.
