What Is A Protein Skimmer?

Copyright Blundell. For very large aquariums it is recommended that you have a very large skimmer. These skimmers often require a separate space since they probably won’t fit inside the stand or sump area.

protein skimmer is a mechanical device that helps to remove organics from the water. Home aquariums are often very high in organic levels. Much, much higher than you would find on a natural reef. One way to help remove organics is by protein skimming. In fact, second only to water changes, I can’t think of a better way to remove organics. Here is how it works: Water is pumped from your aquarium into a big tube and from the tube back into your aquarium. Of course, inside the tube is where the magic happens. A large amount of air is mixed into the water column creating millions of tiny bubbles. These little air bubbles "stick" to the organics in the water and, as the air bubbles rise, they carry the organics with them. This produces foam, which is collected and thrown away. The process is exactly like you see when waves crash on shore and foam is washed onto the beach.

Who Needs a Protein Skimmer?

A protein skimmer is not for everyone. However, it is almost always helpful even for those who do not necessarily need one. The best thing you can do is to analyze your system and see if you are currently providing enough filtration for your specific animals. In reef aquaria, this is almost impossible without a skimmer. Simply put, skimmers are a staple in reef aquaria.

Let’s assume you have a 125 gallon aquarium with 50 pounds of live rock. Let’s also assume you have 3 small fishes. With a healthy refugium and small feedings every couple days, this aquarium will probably run hassle free for years without a skimmer. Now let’s assume you have a 30 gallon aquarium with 4 tangs, 2 angels, 2 anemonefish, and 3 wrasses. You may feed this aquarium daily. This aquarium would almost certainly be better with a skimmer. In fact, it would be irresponsible of me to suggest otherwise.

Your Skimmer Needs

Copyright Blundell. Skimmers can be adjusted for how "wet" or "dry" they run, which means how high up the water level is in the skimmer chamber. You can adjust how easily they "bubble up" and remove waste particles.

This is the tough part. If we stick with our previous example on the 125 gallon few fish vs. the 30 gallon with many fish we can instantly see a difference in bioload. Now let’s add another factor to that example. If the 30 gallon aquarium is intended to just house fishes with some live rock, then an "average" skimmer may do fine. If the 125 gallon tank is intended to house many small polyp stony corals then it may need a very large skimmer, even though it doesn’t have many fishes.

Did you get that? AQUARIUM SIZE IS IMPORTANT, BUT SO ARE THE REQUIREMENTS OF THE LIVESTOCK. Therefore you can’t easily rate a skimmer for a tank size. This is frustrating for many hobbyists. I get phone calls from people asking "Adam, I have a 180 gallon tank. What skimmer should I buy?" I have no idea how to answer that. Do they have a lot of rock? Do they have many fishes? Are they keeping corals? How often do they feed the tank?

Selecting a Skimmer

As a way of helping hobbyists select a skimmer, most manufacturers rate their skimmers for tank size. Again, this is difficult to do, so they make some assumptions and do the best they can. If a company is selling a skimmer and it is rated for a 120-150 gallon aquarium, they are assuming you actually have a tank that size with a few fish, some corals, a clam or two and feeding once each day. Some skimmers come with multiple ratings. The company will say something like "good for 100 gallons of fish only, 75 gallon reef aquarium and 50 gallon small polyp stony corals." No matter how the company rates their skimmers, you still need to consider how your tank compares to the rating system.

Take a look at your system. Do you have a sump area to hold a skimmer? Will you need a skimmer that hangs on the back of the aquarium? Do you have a separate fish room with all your equipment that could house a large skimmer? Start with some of those basic tank design questions. Your answers will help narrow down your choices for skimmer brand and design.

Now you can look at how large of a skimmer to purchase. The general rule is buy as big as you can. But again, this is a great opportunity to ask yourself how much food you are putting into the aquarium, how many fish you have, what other filters you have running and all those sorts of things.


Copyright Blundell. A skimmer provides visual evidence of its work. Unlike the process of liverock breaking down waste, you can see exactly how much your skimmer is doing. It is important to frequently clean out the collection cup and the neck that leads to the cup. This greatly enhances skimmer performance.

A few final thoughts. Home aquariums have far higher nutrient levels than wild reefs. So there isn’t much fear in over-skimming. Second, you can easily add more food, but you can’t easily remove more waste. So if your tank is "too clean," that is very easy to fix. What is a real nightmare is when your tank is just too dirty. And a final third point I want to leave with you is the idea of catastrophe. There will indeed be a time when you will lose a very large soft coral. When something like this happens it would be great if we could just turn on an extra 5 skimmers. So while your skimmer may be able to handle the daily filtration of your aquarium, it may not be able to handle a large problematic day. This is yet one more reason to have an oversized skimmer to help in those rare, catastrophic days.

Author Information
Adam Blundell M.S. is a hobbyist, lecturer, author, teacher, and research biologist. Adam is the director of the Aquatic & Terrestrial Research Team, a group which bridges the gap between hobbyists and scientists. Adam can be reached by email at adamblundell@hotmail.com.