I've set up my tank end of March. I've gone through diatoms, green dust algae, and most recently cyano.
In the spots with highest flow and lighting I noticed some purple spots. It's not getting blown off with a baster like cyano so I suspect coralline. Isn't it too early though?
They can be on a frag plug or on a snail and it could spread and grow in your tank. However, its depends on your parameters on how long it can survive and spread in your tank.