Green coralline-like circles?

[Claw Atticas]

I thought nothing of this round circle when I first spotted it on my glass, thinking it might be some kind of algae growing, but then another one appeared on my overflow box. Another intriguing thing about it, is that it seems to be white underneath the green. It's almost completely flat, and hasn't moved since I first spotted it... anyone have any ideas?


This one includes the reflection through the glass

 

[Fluff]

Looks just like green coralline algae. I wouldn't be concerned.

 

[Tank2379]

Well from what i've read coralline comes in red, green, maroon, purple and orange from what i've read from another forum but i don't know how true that is

 

[Kurt_Nelson]

It's true.