AMEE,
If your tank is not an aio with a surface skim outlet you will accumulate skum on the surface of your tank water. I had to take my sump offline for a couple of months and my surface water was no longer being skimmed into my overflow. This is what I used to pull gunk off the top and bring it under. This lets proper gas exchange on the surface, something you need since you don't have a skimmer. The only problem is the scum is not removed it is just turned under:
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=27119&prodid=56072&catid=2007
If your tank is not an aio with a surface skim outlet you will accumulate skum on the surface of your tank water. I had to take my sump offline for a couple of months and my surface water was no longer being skimmed into my overflow. This is what I used to pull gunk off the top and bring it under. This lets proper gas exchange on the surface, something you need since you don't have a skimmer. The only problem is the scum is not removed it is just turned under:
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=27119&prodid=56072&catid=2007