Coloration on dry live rock

[salzik]

I have had a bunch of dry live rock in my tank for about 8 weeks now. It's all cycled and I have a few fish that have survived for about 3 weeks now. The tank is near a window which gives the tank some indirect sunlight and I've been able to avoid an algae bloom so far. However, I have noticed within the past few weeks that the side of my live rock that faces the window have changed color to a golden brown color. The side of the live rock that does not face the window has not changed color at all. I don't mind the actual color, I'm curious what this change of color is. Is it something I should be concerned about, or is it something normal. Check out the attached pics.

[salzik]

This first pic is the side of the rock facing the window (golden brown in color) and the second pic is the face of the rock not facing the window (off-white color).

[Ryan S]

It looks like diatoms on the side exposed to the light. Perfectly normal. They will go away with time.

[schenktank]

yup thats normal.

[rioreef]

You mentioned facing the window, is direct sunlight getting into the tank? Not a good idea to have that happening from increased algae blooms to increasing tank temp.