Coralline algae?

[Shpanda88]

I started noticing brown speckled stuff growing on my rocks in the highest flow areas of my tank. It is super hard to scrape off and kinda feels more like coralline.
I have only had red coralline grow for the most part mainly on the back glass.
Is brown coralline a thing or is this something bad?

 

[BanjoBandito]

Coralline can start out as green, but if it's brown it's usually a sign that the algae is forming but has been quickly overtaken by something else, typically diatoms. Usually it appears in higher Mg levels, around 1300, in mass. Is the brown stuff "slippery"? If so, it's probably lobophora. It's often confused with coralline, but is brown.