So i got a 90 Gallon tank and put live rock, about 175lbs which i got from someones tank and 80 lbs of reef live sand from my LFS. Its been running for about 3 weeks and i have not seen any changes in ammonia or nitrites. I was told that i would need fish to start the cycle but also that the live rock and live sand would do the job as well. Is there something that i am missing here. Any help is appreciated.