I use dichlor with N2 (and ozone). I test with a 5-way test strip: Free chlorine, total chlorine, ph, total alkalinity, calcium hardness. Used to use Taylor kit (basic one). I consider chlorine my primary sanitizer. I think of ozone and N2 as "supplementary" programs. I haven't any conclusive evidence that either make a large difference, but scientific studies seem to indicate that they help. I don't believe either one should be used without chlorine. My water is always crystal clear. I used to "micro-manage" my water...not any more. Easy, and safe treatment. I stopped with MPS because of suspected skin sensitivity, and use dichlor only for my shock. Vinny's right on the money IMO...
Steve