Typically, you need to do water changes to get nitrate out of the system until you have nitrate controlling microorganisms.
1- Where did you get your rock from? Was it kept wet?
2 - What was your source of water? Tap, RO
, Store bought?
If you're using tap water, do a nitrate test on the water straight out of the tap.
3 - Do you have any livestock in the tank?