For calcium, magnesium, phosphates and alkalinity I use salifert. Pretty accurate and easy to follow instructions. You can actually see the color change distinctly and know what the reading is, unlike with api calcium for instance, you never be sure when the color changes it's so subtle. I bought the hanna electronic testers for alkalinity and phosphate and I use them now since they are literally idiot proof. LOL Just pops up a number and youre done. But they can be a bit pricey.
Check out this link, they have a special price on salifert tests
Professional Testing Kit Package
The saliferts can be pricey too but I slowly bought one like every pay day til I had them all. LOL
red sea are supposed to be quite good as well, just havent tried the new tests they offer yet. Which ever option you go with it;s gonna be $$$ but in test kits you do get what you pay for.