Hard Green Algae

I'm having some algae bloom on a couple rocks that has gone from light to slightly darker green and is a lot like coralline algae in the respect that I can't seem to phase it with a toothbrush. I can scrape it off with a fingernail though. I've heard someone somewhere say that earlier stages of coralline growth on a rock can be green.. The rocks I'm seeing this on have little or no previous coralline on them.. Ideas?

 

It looks like coralline algae to me pic not that clear though

 

My first reef tank about 10 years ago had dark green coralline.
I was told that is was rock from Florida. Not sure if thats true or not. It looks like what you have.

 

I'm kind of curious too. I have the same green hard algae growing on my glass and the only way to clear it is with a razor blade scraper. I have the purple coralline growing in on my rocks as well.

 

There are many species of coralline algae and some of them are green. Due to the intensity and spectrum of light we use in our reef tanks, more rare colors like orange, green, dark maroon, etc. tend to die out and be replace with pinks and purple species.

 

mirco green hair algae