I'm a frugal person (*) that doesn't like to buy things twice and I've read that the API tests are pretty bad and the Salifert are good. Is that true? The part that confuses me is that there are quite a few Salifert tests and they all seem to be sold separately. So what do I really need? What is nice to have? Thanks! * Okay, fairly frugal -- I am into potentially expensive hobbies .