red algea on top of my purple coraline algae
 

My rocks are fully covered with purple and all of an suddenly last week I started to notice that some red algae is growing on top, its hard(try to scrap it with my steak knife, it wouldnt come out) just like purple coraline algae I asked Janett from AO sinces her display tank has the same thing and she told me that its a great/good algea. just want to comfirm with some pro from here. i took some pics but its hard to notice because its just starting to grow. please help I dont want this thing to take over my purple coraline!!!

coraline comes in alot of colors. i have tons of red, pink, purple, and even green in my tank.

anyone can explain why all of a sudden the red coraline is growing over my purple coraline?

natural progression, soon, the purple might grow over the red
Whatever achieves doninance with your current light/water parameters