Hi,
I am cheering for the airstone side...because I have one
Basically, it is a big PVC 4" X 5 feet tube skimmer. I like it a lot and it works pretty well. The air pump is a bit loud compared to other equipment in my tank, but my Mak4 is louder than my air pump.
The main advantage of the airstone type is the contact time -- which is in the order of a couple of minutes. Airstone allows individual control over water GPH and air. Downdraft do not have as much flexibility. However, airstone requires monthly airstone replacement, while Downdraft do not. Power consumption of the downdraft is very high.
So, which is better ? If both skimmers were sized properly for the given tank, probably the airstone would do a better job. Only problem is tha it won't fit under your stand (another problem) and it would be bigger than the downdraft..
The advantage of clear skimmers is air/water mixture tunability. In some instances, too much air in the skimmer degrades performances (turbulence). It is more difficult to detect these conditions in a opaque skimmer than a clear skimmer. Water level adjustments are easier to make in a clear skimmer.
Hope that helps.
- Victor.