Dark green moss?

[freefour]

Hey everyone , I was over at a friends house and he also changed his substrate to sand but now he is getting a kind of dark green moss or fungus growing on top of some of his ornaments .His tank is similar to mine in that he has the same type of dayglow thingys for the fish to hide or swim threw (see my picks) Any suggestions , should he get a snail or allege eater?

 

[QTOFFER]

If the algae is fuzzy, it's annoying, but harmless hair algae. Siamese algae eaters and flagfish definitely eat it.

If the algae slimy , sheet-like, or bubbly, tell your friend to remove a small sample of the algae and smell it. If it stinks to high heaven, it's blue green algae. This stuff is a nightmare because it will completely cover everything in days. A complete blackout (lights off, and tank covered with a blanket) for four days will usually kill it.