algae on top of rocks only

[CubanHogFish]

Hi i would like to know if any one can help. My tank has been up and running for 16 weeks now, I started my tank with dry rock and "live sand" (the bags of sand didnt have water in them). Ive seen many live rocks in other peoples tanks and in my lfs now none of them look white like mine i see that they all have algae on them i guess that what it would be, dark in color and even have some purple in in it. (corraline algae) I dont know if this is normal or am i having a problem with my tank. I do run GFO in my tank and also my ammonia,nitrite and nitrate are all 0 ppm here are 2 pics

 

[Reefing Madness]

What is your phosphate reading? PO4? Looks like normal beginners tank algae to me also. But if your phosphates are a little high, then taking them down a bit would help. Should read between .03-.05

 

[CubanHogFish]

Haven't checked I noticed this morning before going to work I would have to check it when I get home

 

[CubanHogFish]

II also do 2 20% water changes a month

 

[Reefing Madness]

The 20% water changes won't do you any good if that number is to high. But, you need to find out what it is first. I would think at the beginning 20% every 2 weeks is fine, but you'll probably end of doing them weekly to keep your numbers inline.