If you are showing 0 nitrate, your tank is not yet stable. I would wait until you get at least a reading of 10 ppm or so. What type of test kits are you using? If you are using test strips, ditch them and purchase titration/liquid test kits. I recommend API test kits. I like to buy them separately, but you can purchase a master test kit. Are you testing for PH? Do a water change the day before you plan to add fish. How exactly is your set up, as far as what type of filtration, and are you keeping live plants or artificial decor? What are you using to dechlorinate your water? I recommend Seachem Prime. It should be the only one you use. If you have been using something else, get Prime next time when you run out.;-)