is the CC already in the tank? I think you can put a sand layer for a DSB
on top of CC, but don't quote me. Usually a "sugar" grained sand is employed for a DSB
, I think I remeber reading that CC is a nitrate trap, but I'm not certain of this. Aqua-C is expensive, but don't go cheap on a skimmer.
Closed loop you don't need, it's just nice to have. I don't like the look of powerheads in the tank so I'm building a closed loop.
here's a quik schematic at what it looks like, although the drawing i did has the intake and outake spun 90 deg. so nothing was superimposed in the drawing, this is what it is.