White frosting on live rocks

[rsach]

Any idea what this white coating on my rocks is? Tank is 6 months old. I used Marco rock, so don't think this can be dead Coraline algae. I tried scraping it with a toothbrush and it barely comes off, just a few particles when scraping.
All parameters look fine. Corals look healthy.
Temp 79F
Salinity 1.025
Ph 8 API
Ca 440 Salifert
Mg 1440 Salifert
Nitrates 0 ppm API

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[Spieg]

Hard to tell what is white in those photos, but coralline algae will turn white when it dies.

 

[rsach]

Hard to tell what is white in those photos, but coralline algae will turn white when it dies.

All the blueish looking frosting on the rocks is actually white. I used marco rock so I don't think it is dead Coraline algae

 

[Spieg]

How old is the tank? Coralline will grow on man-made rock, it just takes a while.

 

[rsach]

How old is the tank? Coralline will grow on man-made rock, it just takes a while.

It's about 6 months old. Can Coraline start off as white?

 

[Spieg]

Usually it is pink or purple.