Protein skimmers are pretty much mandatory for a reef tank. Although some have claimed success with true Jaubert style tanks and others have run successful reefs with large carbon filters, the protein skimmer is still considered top dog along with the Berlin Method.

Skimmers strip dissolved organic particles from the water before they can decay to ammonia and convert to nitrates through the nitrogen cycle. These DOC's include proteins, amino acids, fats, and other organics. They usually come from wastes produced by the oganisms living in your tank.

Types of Skimmers

Air-driven protein skimmers use a wooden or glass airstone to produce bubbles in a column of water. In hobbyist terms, we usually call these guys counter current skimmers. At one point co-current and counter-current was a big debate. These terms refer to the rotation of the water inside the skimmer. I don't think anyone cares too much about this debate anymore. Air driven skimmers require periodic (monthly) replacement of the airstones, a strong air pump to drive the airstones, and a small water pump to move water in and out of the skimmer.

Venturi skimmers use a venturi valve to inject bubbles into the water column. This takes the place of the airstone in the air-driven skimmer. A high pressure pump is used to pass water through a venturi valve. As water is passed through the venturi valve, it draws in air which produces fine air bubbles inside the skimmer. Another type of skimmer is the recirculating skimmer. These skimmers use a second pump to feed the main skimmer pump. Water is removed from the reaction chamber and sent back through the venturi. The concept here is that by recirculating the water through multiple passes through the skimmer, you can remove even more DOC's. Venturi skimmers require a high pressure pump to run.

Downdraft skimmers send high pressure water though a column of bioballs. An air injector adds air to this mixture and the air is thoroughly mixed with the water as it passes through the column of bioballs. Downdraft skimmers require a high pressure pump to run.

Other: There are a few skimmers on the market today that don't really fall into any of these categories. Mostly, these skimmers use a "needle wheel impeller". The needle wheel impeller replaces the impeller in your skimmer pump. Air is drawn directly into the pump and the needle wheel chops the water and air into a fine mixture. The end result is that it works similarly to a Venturi design, it's just a different method of injecting the air into the water. These skimmers generally are supplied with a specialized pump for the application.

How Skimmers Work

Skimmers work by creating a "foam" or "froth" in the reaction chamber. This froth is an air and water mixture. Now, to remove DOC's (dissolved organic compounds) we use a simple trick of chemistry. Many of these DOC's have a hydrophobic and a hydrophyllic end. The hydrophobic end is "afraid" of the water bubbles and thus is repelled by them. The hydrophyllic end "likes" the water bubbles and is attracted to the water bubbles and rises in the column of foam. The foam, rich in DOC's spills over into the collection cup. This foam is green or brown and smells pretty bad. After watching a protein skimmer in action, it's easy to see the benefits of owning one for your reef tank.

Skimmer Maintenance

Clean your skimmer. Skimmers work best when they're clean. That brown nasty stuff is going to accumulate in the collection cup. Dump it out at least once a week. Wash out whatever has accumulated in the reaction chamber as well. Once a month, take the skimmer out of service and give it a good cleaning.

Clean your pump. If you're using a prefilter on the pump, rinse it out when you clean the skimmer. Check the impeller once in a while for damage and/or wear. If you're dosing kalkwasser, calcium deposits tend to form in pump housings. These can be scraped off with a toothbrush or you can run the pump in a water and vinegar solution. The vinegar is acidic and will dissolve the calcium deposits.

Clean the venturi. Venturi valves tend to clog up. An easy way to unclog them is to run a few cups of warm freshwater through the air intake. The venturi valve needs to be kept relatively clean to function correctly.

Change your airstones. Air Driven Skimmers require periodic replacement of the airstones. A good interval for this is once a month. You may be able to get away with every other month. When the airstones get old, they tend to clog and not produce nice fine air bubbles.

Check your airpump. Air Driven Skimmers need a strong supply of air. If your skimmer isn't functioning properly, your air pump may no longer be putting out sufficient air pressure to run the skimmer. Most quality airpumps can be easily "rebuilt" with new diaphragms which will bring their performance back to nearly new.

Tuning your skimmer

Tuning the skimmer involves adjusting the water flow or airflow to produce a dry foam.So how do you tune the skimmer to produce a dry foam? Usually, it involves regulating the airflow. On an Air Driven Skimmer you'll adjust the output of your airpump, on a venturi model you'll regulate the airflow going into the venturi, needle wheel impeller skimmers will have an air adjustment as well. Downdraft skimmers will have a gate valve to regulate water leaving the skimmer.

One very important part of tuning your skimmer is allowing the skimmer sufficient "Break-In" time. New skimmers that are just placed into operation do not function properly. Before they'll start to work, the inside of the skimmer will need to become coated with a film or slime from your tank water. This can take anywhere from a few hours for a few days. During the break in period, the skimmer won't be producing normal skimmate. So it's very important not to try to get the skimmer functioning corretly from Day 1. Give the skimmer time to break in, and once that has happened, begin tuning the skimmer. An important piece of advice: If you are sending too much air through a new skimmer and it decides to start producing skimmate, you can wind up with a pretty big mess. So, when you first start running a new skimmer, be conservative with how much air you're sending through it.

Choosing a Skimmer

This is hard. There are a few hundred makes and models on the market today, and a new "bigger and better" model is always being introduced. This is also the most important piece of equipment you will buy for your reef tank, so choose wisely. Take the manufacturer's "recommended tank sizes" with a grain of salt. If a skimmer is rated for a 100-200 gallon tank, it may not perform very well on a 180, but might be a great skimmer for a 90 gallon tank.

Also keep your maintenance habits in mind. An air driven skimmer is most often the least expensive solution. However, they do require the most maintenance out of the types listed above. Venturi, Downdraft, and the "other" skimmers generally require far less maintenance, but are more expensive and require dedicated pumps which add to the cost as well.