purple stuff

It looks like branching coralline algae to me.

+1 Smitty, let me say that many people confuse them with montipora. It can be either Hydrolithon boergensenii or Peyssonnelia sp. both are calcareous algae which means they use calcium to grow so, if you want your rock to be covered with it just keep your alk, calcium and magnesium levels stable. I think yours looks a lot to Hydrolithon boergensenii. If it is, they are known as bio-indicators, and they help biologists to have an idea of how stable water quality is in a "x" area.
 
Back
Top