In our quest to provide the best water quality for our aquarium inhabitants, the Protein Skimmer is a useful tool for most marine aquariums. In its simplest form, the skimmer does exactly what its name implies; it will skim proteins (organics) from the water and completely remove them from the aquarium environment into a “collection cup”. This is an important point to understand. There are other filter medias that will trap or remove the protein from the water, but if they are still in the system (located in a filter or sump) the bacteria can still get to the protein and digest it to produce more nitrates. (Purigen is an exception to this, as it denatures the protein when attached to prevent bacterial digestion.) Protein Skimmers will prevent additional nitrate wastes from being produced by excess wastes in the water.
Over the years, skimmers have gone through many design changes and are available for most any size aquarium, from a Nano to tanks with hundreds of gallons to complex holding facilities at wholesale operations. Skimmers work because proteins are charged molecules and have regions that are hydrophobic that cause them to try to extend this portion out of the water. If we can mix air bubbles with the water, the proteins tend to stick to the bubbles and, once enough of them are attached to the bubble, the bubble will not easily burst. These “dirty” bubbles will tend to accumulate at the top of the reaction chamber, and, as more are produced, they will start to push the top bubbles out of the neck into the collection cup. The very basic skimmer is purely an air driven unit placed inside the aquarium. A stream of very fine bubbles is injected into the bottom of the skimmer reaction chamber and rises through a counter-current water flow to the neck of the collection cup. The counter current allows for a longer “dwell time” as the bubbles have to fight the current. The longer the bubbles are in contact with the water, the longer they have to collect proteins as they rise. These air driven systems require a separate air pump (too noisy) and a lime wood air stone (needs replaced every 3 months) that make them less efficient than the newer designs that use a water pump and a venturi valve to inject the air into the reaction chamber along with the water.
Venturi systems allow the skimmers to be scaled from smaller sizes for aquariums less than 50 gallons to monster systems capable of handling 1000’s of gallons by increasing the size of the reaction chamber and the flow of the pump. Visit a wholesale operation, and you are likely to see skimmers 10-12 feet tall with a 6 foot diameter attached to large rows of holding tanks. A fairly recent development is the use of a specialized “needlewheel” impeller, which draws the air into the intake of the water pump to create froth of micro bubbles to make the skimming even more efficient. The needlewheel blades chop the air into tiny bubbles that flow with the water into the skimmer reaction chamber. This design greatly decreases the rate of the water flow through the pump, so many designs using needlewheels also have to have a circulation/flow water pump to physically push the water through the skimmer chamber. And in the tradition that more is better, there are now designs that attach additional needlewheel pumps to the reaction body to recirculate the water from the reaction chamber, through the pump, and back to the reaction chamber. This increases the number of fine air bubbles and the contact time in the chamber to increase efficiency without the need to make the reaction chamber larger. Protein skimmers can also be used as an ozone reactor if ozone is injected into the air stream. The longer contact time increases the efficiency of the ozone to reduce organic wastes and possibly kill micro-organisms. You should be aware that the use of ozone to chemically reduce the wastes will cause less production of wastes in the collection cup.
Before you rush right out and get a protein skimmer, be aware that they will require a fair amount of monitoring to ensure proper function. The air injection might need to be adjusted every time you add any chemicals to the water or make a partial water change. On large scale aquariums, the reduction in the production of nitrates will allow for fewer water changes and fewer water changes can eventually help pay for the skimmer!