purple algae turning red

[krrector]

I have a twenty nine gallon reef tank. It has been set up for about a year. I have lots of live rock and only a few fish. I have noticed that the purple algae on my rocks is turning a deep red color. It is also forming on the glass. It is taking over the purple algae really fast. I have checked and everything tests out fine but was just wondering the reason. Any thoughts would be greatly appreciated.

 

[fender]

Coraline algae comes in more colors than just purple - I have had orange and red but it grows very slowly and usually dies off or gets covered by the purple. Is it hard and crusty like the purple? Are you sure it is not a cyano breakout?
If it is red coraline, then congrats, very few aquariums can sustain anything other than purple (it requires less light). If it is slimy, then you have a cyano breakout most likely and need to check for high nitrates, phosphates etc.