Is this coraline or something more sinister?

[Axemanian]

Saw this today, not sure if it’s coraline or cyano or what...
There was some coraline on a hermit crab shell that I scraped off a few weeks ago when he swapped shells and I sprayed it over the rocks, but seems a little early for the purple stuff... tank is 75g and 10 weeks old...
thoughts?

 

[JGT]

Looks like the start of dinos or cyano. To be expected given the newness of your tank.

 

[Axemanian]

Thanks JGT, hope it’s just cyano...

 

[Llg]

Mine looked like that at 4 weeks and it was coralline. Hopefully that is what you have.