I won’t bore you with the nitty gritty principles of how it works but it is an integral piece of equipment for captive saltwater systems. To summarize it all, protein skimmers incorporate air into water in a manner where the resulting foam, consisting of dissolved organics, is pushed up the tube and collected in a cup.
Here’s an experiment you can do to get an idea of how a protein skimmer works…
…take an empty water bottle and fill it ~1/3 full with water. Put the cap on and shake the “heck” out of it. You will see the bubble dissipate rather quickly.
Now, the gross part…
Like in the movie “Ace Ventura: When Nature Calls”, you know that scene…spit into the water bottle, cap and shake vigorously once more. The bubbles will stay intact longer. Collecting the resulting bubbles, will remove some of the dissolved organics, which is the spit.
Is a protein skimmer integral for smaller systems of less than 20gallons?
Provided that water changes and the replacing of exhausted/near exhausted chemical media are performed regularly, one will find that this method is just as effective as skimmers for this size of aquarium.
For the most part, the smaller skimmers don’t perform very well and the better ones cost almost as much as quality in-sump skimmers. So spend that money on salt, supplements or whatever else is needed to maintain water quality. If you have a habit of over feeding or have a heavily stocked system that must be heavily fed, then considering a quality skimmer may be a worthwhile investment as water changes of more than once a week can quickly become a chore, taking the fun out of it.
Based on the principles of the venturi effect, water pressure is reduced when it flows through a constricted section of pipe. A pump pushes water through one of these devices and air enters at the restricted portion, mixing air and water as it enters the skimmer. Finer air bubbles are created if a pressure rated pump or high volume flow biased pump is used.
2. Aspirating: Needlewheel/Meshwheel/Pinwheel
Similar to the venturi style, the pump is placed after the venturi and the air drawn in are coarser than the venturi and a high pressure pump is not required. The impeller blades are replaced with a disc of pins pointing parallel to the flow of water into the pump, a disc of a mesh material or pins radiating from the centre that has smaller pins/stubs sticking out of the radiating pins.
The needle/mesh/pinwheel chops up the drawn air into very fine bubbles, significantly finer if the impeller were just the typical blade style.
A high volume of water is passed through the top of a tube under pressure via a pressure rated pump. The tube is filled with “bio-balls” and as water is forced into the tube, the “pins” of the bioballs “split” the stream of water as it passes down the tube. In the process, air is incorporated into the water.
Similar to downdraft and venturi style skimmers, high volume and pressure is required. A foam nozzle (Beckett 1408, from which the name is derived) is used to incorporate air into the stream of water as it passes through.
5. Spray Induction
Water is “power sprayed” above the water level in the protein skimmer reaction box.. Similar to the downdraft skimmer, when water is sprayed onto the water surface, air is incorporated into the water.
6. Wood Air Stone
This is where it all began. Like typical airstones used in freshwater aquariums, they use limewood or basswood where the fine pores create the desired ultra fine bubbles.
For today’s marine hobbyist, the popular styles are aspirating needlewheels, Beckett and downdraft style skimmers. Choosing which style of skimmer depends on spatial requirements of the skimmer, access for maintenance/service, power consumption, noise level, etc. Choose the brand and any supporting equipment that has a good running track record as well as customer support in your area should any issues arise.