Hmm hair algea
 

What causes this type ? I think that what it is. I have some small patches (size of a nickel etc) and some filiments on side /rear glass. To much /not enough light ?? chemical imbalance

What is your phosphate testing?

One of the better write-ups on hair algae.

http://www.canreef.com/vbulletin/showthread.php?t=44860

Enjoy!