'Forest' on live rock !

[Pirates_Gold]

This is not a clear picture, but looks to be Cotton Candy algae or Asperagopsis sp. Regardless, this is a nuisance algae that needs to be controlled immediately.

You have a few choices as follows:

1. Return the live rock to your LFS (especially if they knowingly sold you another hobbyists problem rock);
2. Remove it totally from your system and cook it for later use;
3. Keep the the live rock, but manually remove as much as possible by scrubbing (in a bucket outside of the aquarium), rinse well and then replace it to your system. Ensure that your water parameters will sustain any livestock, they introduce some herbivores in an attempt to control the red algae. A few that might help you include Sea Urchins, Lettuce Nudibranchs, Mexican Turbo Snails, Foxface and some of the Surgeonfish.

HTH