Back into reefing after a 15-year hiatus. Cycling with dry rock is new to me. Tank is 3 months old, lights have been on for 3-ish weeks, starting at 4 hours a day, now running at 9 hours a day. Put my first corals (some zoa frags) into the tank this week and up pops this single round spot on one of my rocks. It's about 1/2 inch in diameter and it is the only one I can find in the entire tank. Is this coralline algae? Most posts I have seen show very small spots widely dispersed throughout the tank. Would love to know your thoughts. Thanks!