What is this stuff encrusting on my rock?

[huckjai]

Decided to crank the blue lights to 100% tonight for fun and just noticed these two patches encrusting on my rock. Looks cool under blue lighting, but ugly under white lighting. No clue how it got on my rock. Is it some sort of coral? It's encrusting my rock like some corals do. Hope it's not something bad.

Thanks.

 

[jurgenph]

looks like cyphastrea


J.

 

[Tahoe61]

Yup to Cyphastra.