IF!

[EQCM2B]

If it is bright green and IF it is on the glass where there is a good amount of flow and IF it is kind of hard to scrape off, would you think that it is coraline? I have pink, and purple already on the rocks but this stuff is on the glass and does not scrape of very easy.

[davejnz]

There is a green calcareous/coralline algae.However,I think the green algae that grows on the glass that wont scrape off is something else.I'm not all that familiar with the different scientific names of micro/macroalgaes so maybe someone else can chime in.

[Amphibious]

It's probably Diatoms.

[EQCM2B]

All I know is that a razor blade has a hard time scraping it off. Luckily it is a glass tank.

[davejnz]

I don't believe its Diatoms.They grow as a brownish film that is easily scraped off with a magnet cleaner.This type of algae can only be removed with a razor blade IME.It looks exactly like tiny green algae dots that are left behind after your magnet cleans off the Diatoms.It is not a calcareous algae,I have green coralline algae in my tank and it doesn't grow the same way as coralines do.I believe it to be a type of turf algae.Hopefully one of you algae gurus can chime in here with the proper name for it.

[butterfly_babe4200]

I have it also. Never thought twice about it. It is all over under the filter in the back wall.

[Sweetpea]

I've got it, too. The closest I've come to getting it off was when I got a few grains of sand caught between my scraper and the glass....

[KG]

That's coralline.

KG