Algae/Sponge issues

[Yemstar]

Hi All,

I'm new here and really need your help.

My tank has been set up for about 6 months and some form of algae seems to be taking over my tank. The live rock, skimmer and back wall easily gets coated in a brown/green algae that makes everything look dirty.

To make things worse, I seem to have white sponge growing everywhere to the extent that the algae/sponge combo is taking over EVERYTHING.

I have attached pics to help explain what i'm talking about.

My tank setup:

The tank is 70L
2 Hydor Koalia powerheads (1600 & 900)
external octo reef skimmer.
Maxspect 120W lighting which I have turned down (its now at about 45% max during its peak for about 4 hours).
5" sandbed with live rock.

I do weekly water changes and everything in the tank seems fine but it is just getting out of control.

What can I do? I guess maybe I need more of a CUC?

[Yemstar]

Wow, sorry for the crazy large images!