The green is taking over..help!!!!!!!!!!!!!!!!

[scott_r]

Ok its bad but not that bad. As you can see in the pic my sand bed is getting covered in area's with what looks like algae with fine hair. Never had this issue this bad till I added an Evergro 2012 and its really took off. I have about 12 nassarius snails, bunch of crabs and other snails (dont know names) My Nitrate is around 5, ammonia zero. I do 15% water changes weekly. I bought this tank off another fellow in town and am unsure how long he had it running but I have had it running well for 4 months. Fish are a yellow tang, 2 clowns and a dwarf lion. I also have a pair of blood red shrimp. All are happy. For corals I have 1 large hammerspawn, zoa colony and a small green cabbage.
Any suggestions on how to control this or is it just part of a cycle?

Cheers!!