A protein skimmer, also sometimes referred to as a foam fractionator, is a piece of aquarium equipment that is primarily used in saltwater aquariums in order to remove dissolved organic compounds (DOC) and other harmful substances that if not removed can breakdown in the aquarium or filter adding to the biological load on an aquarium.  Protein skimmers remove these hydrophilic substances completely from the water using air bubbles that are collected in a collection cup. As air and water are mixed in the skimmer chamber the bubbles rise and take with them the dissolved organics that are attracted to the bubble surface. When the bubbles with the proteins, amino acids and other nasty stuff bubble up the tube into the collection cup they are completely removed from the aquarium. Unlike a mechanical filter that just traps solids but still exposes them to the aquarium as the water continues to flow over them all the while these solids are breaking down and adding to the total bio-load on a tank. Skimmers could possibly be consider one of the most significant advances for the saltwater hobbyist.

Think about the ocean for a minute. You know how as the waves crash on shore you will sometimes notice sea foam? This is similar to the way protein skimmers function. Air is mixed with water and then the dirty bubbles (foam) are placed on shore, only with a protein skimmer this foam is removed from the system via the collection cup.

Skimmer Benefits

• Skimmers increase the dissolve oxygen levels and redox potential in an aquarium
• They remove dissolved organics before they get a chance to breakdown and become a food source for nuisance algae
• By removing dissolved organics the aquarium water clarity does not age or yellow as quickly since the DOC buildup is less allowing light to penetrate deeper into the tank for the benefit of corals and other inverts.
• Can help lead to a more stable pH since less dissolved organics are in the system.
• Overall improvement in the health and vigor of the animals in the aquarium since their wastes are being removed from the system via the collection cup.

Do I really need to a protein skimmer?

One of the first questions new saltwater hobbyists seem to ask is whether they really need a protein skimmer for their first setup. Especially when they start to shop for a skimmer. The short answer is no, you don't have to run a protein skimmer on your setup. There are many hobbyists that run successful systems without them. However, these hobbyists also realize the importance of regular partial water changes for the aquarium and how important water changes are to the health and well being of the animals in their care.

By not running a skimmer you really do need to stay on top of those water changes. Otherwise you will start to see nuisance algae growths cropping up all over the place, especially if you have high output lighting like metal halides, T5's or VHO flourescents. The initial expense of getting a good protein skimmer is justified in the peace of mind it gives the hobbyist and the overall water quality improvement it can provide. I'm telling ya, once you see and smell your first collection cup full of gunk that is removed from your aquarium you will be hooked on skimmers. The way most systems are stocked nowadays (rarely are they under stocked) skimmers should be pulling out at least a cup full of skimmate from the system daily. Do you really want that amount of dissolved organics accumulating in your tank in between water changes? Me neither.

Running a system without a skimmer and without live rock would seem to be someone that is just trying to A) set themselves up for failure or B) they like bashing their heads against walls. If you're planning on a system without live rock and no protein skimmer I would simply ask, why? Make the system as easy to maintain as possible and chances are you will be able to enjoy it more.

Skimmer Types

Really? You want to cover this? Ok, if you say so. If your mind starts to glaze over mid-read, you've been warned. Basically, the object here is to find the best way to create lots of tiny bubbles and to provide the optimal contact time with the organics so they can attach to the bubbles and then rise as a foam into the collection cup. The body style of the skimmer can be an important design consideration when utilizing any of the methods of creating bubbles. Here are a few ways to make bubbles:
Co-current skimmers: These were some of the first used and they had an air stone at the bottom of the chamber providing the air bubbles. The air bubbles rose vertically and were collected into a cup. Actually, these skimmers even today are good skimmers. The wooden air stones (finer bubbles) just have to be replaced regularly.

Counter Current skimmers: The air/water mixture is forced through a counter-current of aquarium water in the body of the skimmer. This is supposed to give a longer contact time for the bubbles to attract the organics.
Venturi skimmers: These use a venturi valve to mix in air with the water. These valves are usually situated on the intake tube coming into the skimmer.
Needle Wheel Skimmers: These use a spoked wheel that spins and chops up the incoming water producing fine bubbles. There are also mesh wheel skimmers that function in a similar way.
Spray Induction: As the aquarium water comes into the skimmer it is forced through a spray nozzle that creates a lot of tiny bubbles.
Downdraft and Beckett: These skimmer types use proprietary parts to mix the air and water to create the glorious bubbles we love. Some of the larger protein skimmers are these types of skimmers.
Knowing how a skimmer creates it's bubbles could be a consideration for the hobbyist. Some are more popular than others. It really comes down to doing your research, just like everything else in this hobby. Are you going to pick a skimmer just because it's a downdraft skimmer? Of course not. You are going to come to a decision based on reviews from other hobbyists or first Hand experience with a unit.
Skimmer Maintenance
When shopping for a protein skimmer it is very important to include in your decision making the methods and ease of maintenance on the product before buying one.

• How easy is it to empty and clean the collection cup? This is a daily task and collection cup design is a very important factor.
• How easy is it to get into the skimmer with your arm for scrubbing the walls? You won't be cleaning the walls except maybe every 6 months to annually.
• How easy is it to clean the bubble creation device? Can you easily get to it with a small bottle brush?

Cleaning the collection cup should be done daily for optimum performance. As residue builds up on the neck of the cup it can impede the rising of the foam and ultimately the amount of gunk that you remove from the system.
Skimmers can be a valuable asset for your saltwater aquarium. They can help create a more stable environment for your animals and a healthier one too. If you just can't afford a decent protein skimmer you should honestly rethink the whole saltwater thing, at least for now. Especially for a beginner to the hobby our goal here is to make sure you have all the tools you need to succeed while having fun. Save up enough money until you can afford one a later date. You will be glad you did.
One last thing, skimmers are very expensive and the old saying that "you get what you pay for" certainly has some merit with skimmers. Trying to go the inexpensive route will often end up costing you more in the long run. I've been there and done that. Don't waste your money on a cheap skimmer. This piece of aquarium equipment is just too important. Get a good one from the start after researching them thoroughly.