save your money an don't buy an iron test kit. For pH, KH, and GH, the inexpensive Hagen kit should work perfectly fine. Calcium kit should ONLY be purchased if you are having some very perplexing issues that MIGHT relate to Ca. I say skip till you need it. Nitrate and phosphate are another issue. Accuracy IME is much more important here than with the other kits. For NO3, you want the best resolution you can get between 0-15ppm. For PO4, 0-3ppm. Ignore any nitrate kit that goes somehting like 0,10,20,40etc. you want ATLEAST 0,5,10,20 better ye 0,2.5,5,10,20....and similarly to phosphate for the 0-3 range.