I 2nd that, Murf. I don't have much flow at all through my fuge (1700 gph@ ~4ft of head loss and about 8 90 degree elbows). And, the sump is almost 5 feet long, 3 of that is fuge. My chaeto doesn't move at all. No tumbling, rolling, or anything. You'd think it was just sitting in still water at a glance. And, I grow about a gallon size ziploc bag twice a month.
By the way, I use southdown sand in my fuge. Not for nitrate reduction, but for fauna habitat. If you have a good load of macro algaes, they should handle the nitrates fine. My nitrates are undetectable, of course my phosphates are outrageous. I blame that on the 4 daily feedings so it's expected.