sump filtration

[Aquattro]

I have a skimmer in my sump. Once in a while I'll throw a bag of carbon in for a couple weeks. Nothing else. Bioballs are used more for wet/dry filters, and can/do produce a lot of nitrate. Your rock and sand should be your primary filtration with a skimmer cleaning out the gunk. Some people use macro-algae to give additional nutrient export.