It is always tough to measure skimmer performance- I'd would like to mention that raw air flow is not very meaningful without considering the water flow too. While there is a maximum amount of air that can used and still get "foam" (and not just a top-off-of-the-blender effect), some designs can run just fine on far less than that maximum number. I'd suggest that a SCFH/GPM measurement might be useful, but that does ignore the system water volume which I feel has a far greater impact as the well-being of the inhabitants.
The three skimmer traits that have the most impact on how each skimmer performs are:
- Air flow (and associated bubble size)
- Water flow
- Water volume
And to a lesser extent, water path. These all combine in to some useful numbers:
Dwell time- skimmer water volume, divided by input water in gallons per second gives the number of seconds that the average water particle will be "in play" in the skimmer. This is a very rough average, as it depends greatly on the skimmer design. Picture a long tall counter-current tube, vs. a short square box. Both could have the same dwell number, but very different performance. But for similar physical designs of skimmers, this is a good measurement.
Contact length- This is somewhat overlooked, but I feel it is important. This is the minimum distance that every particle of water must travel before exiting the skimmer. For some designs, this could be as little as 6 inches. For others, it is over a hundred. For a full system picture the minimum, average and maximum numbers should be known.
As mentioned above, power draw is a valid concern, but as I've not seen the math posted yet, how about this:
165 watts is 1.375 Amps at 120VAC. Running 24/7 that is 27.7 K watt hours per week, or about 1441 KWH per year. I have dirt cheap power (less than $0.05 a KWH), so it would cost me $1.39 a week or $72 per year to run a 165W skimmer.
Mentioned above is the question "Why do Beckett's not have tapered necks?" As Hahn mentioned, a well designed, high-air flow skimmer does not benefit noticeably from a tapered neck in the 6-8" diameter models that we typically see in home aquaria. For my own designs, the negligible performance difference does not warrant the associated costs to use them.
There are always trade-offs in any design. I've noticed a tendency to assume the manufacturers don't know what they are doing (I do this myself for non reef-related things), but in reality, the big name manufacturers have all spent years trying different things out and selecting the best ideas to build. Look at Frank's article above- how many skimmer neck designs did PM test to find the best one? I've got a whole room full of test mules for various concepts. Some worked better, some didn't. Some worked well but were not worth the costs, as there was an easier way that became obvious during testing.
That's not to say there are not a few "features" out there that are purely marketing speak- try as we might, those sales guys do get in the way of us engineers at times. That's why they get the big bucks though.
Rough list in my suggested order of priority of things that impacts a skimmer's performance:
Tank volume
Tank inhabitants, including algae and any scrubbers (waste generation level, and type of waste)
Feeding regime
Skimmer's water flow / Air flow / Water volume
Skimmer intake/exit (Recirculating or flow-though)
In this thread, we are focusing only on the skimmer air flow, a subset of item 4 on my list, which just is not enough data in and of itself, to determine how a skimmer will perform in any situation.
These discussions are great- I really enjoy seeing the data too- Please keep it up.
