In short, the four main factors which govern a protein skimmer's effectiveness are…
1. Bubble size
2. Bubble quantity
3. Overall flow-thru rate
4. Quality of contact time
Pretty simple, right? Well, it gets more complicated…
First let's talk about bubble size. Smaller bubbles are preferred over larger ones since they offer a larger surface area to volume ratio. Since the nuts and bolts of protein skimming takes place on the surfaces of air bubbles, our goal is to maximize this variable by introducing the smallest bubbles possible. Of course, at some point the bubbles could become so tiny that they would actually stay dissolved in the water and cease to produce foam. For most purposes, it is nearly impossible to generate bubbles this small. The same logic follows for bubble quantity - since larger numbers of bubbles mean increased surface area, we want to inject as many bubbles, overall, as physically possible. Once again, it would be possible to inject too many bubbles (imagine a protein skimmer packed so tightly with bubbles that it was almost "dry". Given the technology available, however, this has yet to become a realistic problem.
The overall flow-thru rate and quality of contact time are not as clear cut as the previous two measures. Some have reported that high flow-thru rates (several hundred gallons per hour) yield the best results. Others argue that a slow, leisurely flow-thru rate facilitates the best skimming. Most likely, both schools of thought are correct in their own way. The actual chemistry behind the mechanism of protein skimming tells us that, in order to remove the maximum amount of waste possible per bubble, we want a very, very slow flow-thru rate. This makes perfect sense… If the flow-thru rate is slow, each individual air bubble can react with the water for a longer period of time. Air bubbles, after all, don't become saturated with proteins immediately. Research suggests, in fact, that they continue to become coated with organic compounds for up to 12 minutes (Harker).
The problem, and this is why the "high flow-thru rate" school of thought is also partially correct, is that aquariums are closed systems which need to be "cleaned" at an efficient rate of speed. Imagine holding a vacuum cleaner over the same section of carpet for ten straight years. Sure, that little square of shag might be extremely clean once you are done, but what about the rest of the house?? Our goal is not to maximize the amount of protein removed per bubble, but to maximize the amount of protein removed per unit time. An efficient protein skimmer, then, is one which removes the largest amount of waste in the shortest time possible. High flow thru-rates are beneficial because they allow large amounts of the aquarium water to be processed rapidly. Although less protein is removed per bubble (because the air and water are not being allowed to react for very long), it is possible to treat the entire tank volume in a short amount of time. There is probably a middle ground which yields the best results. It is important to note that both high and low flow-thru rates can and have been used effectively, and neither method is definitely better than the other. Our own research with different flow rates and air-injection methods suggest that for larger tanks (100+ gallons), higher flow-thru rates are better suited than slower ones. This might be due to the added benefit which high flow-thru rates provide; more thoroughly oxygenated water. The real answer is far from clear, however.
By now you should have a general idea about the main factors which make some skimmers more effective than others. There still remains one very large problem, however, and that is the method. Open the latest issue of FAMA and you're bound to see ads for over ten different skimmer brands. Do they look the same? Heck no! Do they work the same? For the most part, yes. Every skimmer has its pros and cons, however.
Our market research suggests that there are six main factors which are important to customers. These are, in no specific order…
Ease of Use