I like Red Sea for CA, ALK, and Mag they make a kit with all three. The checkers are good for Alk and P04(phosphate) but are junk for CA as you need pure water which is hard to find! I like Salifert for Nitrate or API.
I test Alk twice a week, CA, P04(phosphate) once a week, and Nitrate and Mag once every other week.