API is ok but the test are sometimes hard to decider between shades of green and red. Depending on tests. You need to be testing calcium, alk, magnesium, pH, iodine/iodide, phosphate and nitrate if you plan on running a reef. Calc should be around 420 but not to exceed 450. Alk should be between 8-11 12 is too high. Magnesium should be around 1380 but no lower than 1300 or higher than 1400. Iodide at .06 helps shrimp, snails and herms molt their shells. Phosphate should be at .03 and nitrate as low as possible.
I use the red sea pro test kits as they are super accurate. And they come in combo packs. A little more expensive but highly worth it. The next step up from this line of test kits would be the Hanna checkers but they don't have a complete line for every test yet.