The reason I asked for the differences is because I am following the Bullet Proof Reef examples on garf.org and the Carib-Sea is what they recommend. Their system also uses a plenum, will I have a problem with the finer grained southdown sand going through the screen? Should it still be OK, or should I go with a layer of coarse sand followed by the southdown, followed by LS? or just dump the plenum idea all together?
Since their site is a full set of directions from start to finish using one of the many, many ways to do this, and I am a novice, I want to stick to their directions as much as possible. For example, some people may say that using a filter is a must, or will work in place of a protein skimmer. This may or may not be true, but I'm too new at this to really know the differences myself. garf says protein skimmer only, so that's what I want to do.
So, the moral of the story is that I want to stick with the plenum idea if possible, but save some money on sand if it will be an adequate substitute. Make sense?