As far as I understand, from reading your information about filters, as well as what I already know about freshwater systems. A water change is the only way to get rid of nitrates. The bioballs will hold "Junk" and will cause the nitrates to go up, causing a problem just like gravel that holds "junk" until cleaned (or any other type of filter). The end result of any type of filtration will result in higher and higher nitrate levels until the water change.
I'm sure you know more about this stuff than I do, but am I right so far?
I think Clean bioballs will produce nitrates the same as any other type of filter. What do you think? I'm interested in more ideas about this. If my statement was wrong I'm sorry. I was taught that by a pretty knowledgable guy at one of the local high end fish stores. I have a w/d filter w/bioballs. I felt that was the best kind of filtration that I could buy.