I currently run my carbon passively with a bag in the return chamber of each sump. I change it every 3 weeks so that it does not become exhausted and or leach DOC's back into the system.
I also use the BRS Lignite carbon and like it a bunch.
Check out Grey Seas Aquatics, they aren't a sponsor here yet but they make a very affordable DIY acrylic reactor you might like. Great price, great size over all good product.