qustion about my cycle

[Kirktimm]

mynitrite and nitrate and amonnia is all at 0mg/l. its a 25 gal with aleast 30 -35 pound of live rock and its only w week into its cycle. now i dont want to add any fish or anything yet. question is now why do i have to wait four weeks for this cycle.and i did a water change two days ago... i got my water tested before i did my water change, and the amonnia was higher then the card goes and i got it tested by redcoral, and nitrate and nitrite was higher than 3.3, after that my friend gave me a rock that was crued and i put into my tank, but now after that water change my levels are all at 0?