If you add a big piece of dry (dead) white rock into your tank, just monitor the NO3
... If you get a spike I would do water changes or dose NOPOX.
The white rock will fade into a green, then darker color, and end up live rock after few months. Then coraline will start to grow on it.
Make sure you rinse the rock well before you put it in the tank. I would soak it in a RODI
water bucket for 1-2 days... I use white dry rocks for making frags, but thoses rocks are so small I only give them a little rinse of tap before gluing frags...