Sump troubles

[c_ray00]

I having been running a 20 gallon sump under my 75 gallon tank for about 4 months now and it never has really caught on yet. It seems to be always dirty and the caulerpa hasn't really even grown much. I built it myself so maybe there is a flaw in the design. Let me know what you guys and gals think. I add Iron for the plants and my water levels are all fine including sality.
I will include a graphic of what it looks like.

 

[dreeves]

Caulerpa just doesnt grow..it needs nutrients in addition to the Iron to thrive...if it isnt growing, chances are you have low levels of the nutrients, which is what you are striving for.