How to grow green algae on rocks?

[lloyd378]

I have a real nice white rock in my 125 that recently started growing green algae on it..... I figured out the cause was the fact that I had left the curtains open in that room for a couple of weeks and the natural light made it happen.  i have since closed the curtains as green algae was not what I was going for in that tank.
Here's my rock with the algae

 

[SonicsDC25]

Brown algae seems to be picking up in growth, at least on the 2 same rocks. The rest is still relatively the same. Been cleaning my glass more often as well due to the brown algae build-up O_O

 

[pbmax]

You could always experiment with adding nitrogen and phosphorus to the water? Without any plants that should encourage a decent amount of algae growth. Worst case you'll get a green water bloom, I imagine.