When you start cycling it is a good idea to check daily. After the cycle for the first couple of months at least weekly. I test mine at least once a month now, If one of the fish act weird or coral isn't acting right then I test.
I use API and haven't had a problem with it. The calcium test takes a little getting use to but the only reason I use that is I have SPS. Don't dose anything you don't have a test for.