Hard Red Algae or cyano?

[bobnicaragua]

I have a red algae that is impossible to scrape off, I only break off chunks of coralline underneath it.

I’ve treated with chemiclean twice in 6 days. This isn’t the soft Cyano I’ve had before that chemiclean wiped out in less than 48 hours.

It’s receded a little on the back glass, but now spreading on the rocks.

Nitrates 2
Phosphates .07

 

[Jekyl]

@vetteguy53081

 

[GarrettT]

Looks like coralline algae to me.

 

[bobnicaragua]

Looks like coralline algae to me.

I guess it could be, it’s hard enough, but it has receded on the back glass since I dosed chemiclean.
The overflow was completely covered, now there are uncovered spots.

 

[vetteguy53081]

Its a calcareous organism similar to coraline known as Lithothamnions

 

[GarrettT]

I have it on mine, always have.

 

[bobnicaragua]

I’ve had spots on the rocks, but never had it spread all over the tank.