When your cycle begins, the first thing to spike will be your ammonias. Free-floating protein in your water is broken down into ammonia, and thus begins the toxicity. Next, the ammonia is broken down into nitrites, and from there into nitrates. Nitrates are what linger in your tank and are removed by water changes, unless you have a DSB, which will slowly remove your nitrates. I'm assuming since this is your first time to test water that this is a new tank setup? How old is it and how much sand and rock does it have? Also, have you added anything to the tank, such as fresh, uncooked shrimp, to start the cycle?