You hafta do something to start it. Live rock will start it . But another popular method is to just simply throw a piece of shrimp in your tank...Yep, the kind you eat...only not cooked. You want something in your tank that will rot and cause an ammonia spike. The ammonia is "converted" to nitrites then those to nitrates then your parameters will all read 0. You are correct, it will take about 6 weeks. Using live rock to cycle your tank will usually accomplish this in about 2 to 3 weeks.