If you’ve even considered setting up a saltwater aquarium you’ve probably already heard the words “protein skimmer”. But what is a protein skimmer anyway? Essentially it’s a type filter. It removes organic compounds before they have a chance to break down and further degrade the water quality or fuel algae growth. But instead of using a filter pad or something like that it employs something know as foam fractionation. Basically, the waste molecules that a protein skimmer excels at removing are bipolar, meaning they have an unbalanced charge. In the context of the aquarium this leads to one end of the molecule being attracted to the water while the other end is attracted to the air. And where these two things meet, as in the surface, the molecule is happiest. The part that likes the air sticks out while the other end stays in the water and the molecule floatss around like a tiny iceberg.
So how can we use this property of these molecules to our advantage? Bubbles. Lots and lots of bubbles. Bubbles are basically a bunch of air/water boundaries for these molecules to settle into. And as the bubbles rise to the surface they drag the molecules with them where they pile up and accumulate into a thick foam that can be easily skimmed off. And there you have it- protein skimmer!
So what makes a good skimmer? At its heart the goal of any good skimmer is to create as many tiny bubbles as possible for the tank’s water to react with. There are only so many ways to make a bubble, but even so several different designs have emerged over the years that each function in slightly different ways. When picking out a new skimmer knowing the terminology and what these differences are is important to keep from getting lost in a myriad of options. Let’s run through the basic types:
A very simple and outdated design, air stone powered skimmers are basically just an air stone, usually made of a fine grained wood, mounted at the bottom of a long tube. Water flows through the tube and the air stone bubbles to create the foam. Air stone skimmers are rarely used anymore as they just aren’t that efficient compared to the other options available today and area a real pain to maintain.
The basic idea in a downdraft skimmer is that water is injected at high pressure with air into a tube filled with bio-balls or some other plastic media. When the high pressure water and air hits this column of media a ton of turbulence is created resulting in a very fine foam. After passing through the column the foam is directed to a second chamber where the skimming takes place. These are quite effective skimmers, though you’re unlikely to see many of them as the technology is patented limiting their production to only one company.
When liquid flowing through a tube is constricted it is forced to speed up. When it speeds up a pressure drop occurs. This is known as the venturi effect and is key feature of these types of skimmers. Water us pumped at high pressure into a pipe that narrows. Where that narrowing occurs and the pressure drop happens an air line is attached to allow air to be sucked in where the turbulence chops it into fine bubbles. Pure venturi skimmers aren’t very common anymore, but the technology is often used in conjunction with other methods. Beckett skimmers work on the same principle but utilize a more specialized Beckett injector to produce the foam and are more commonly available.
As the name suggests the key feature in these types of skimmers is the impeller in the pump that drives them. Normally the impeller in an aquarium pump has several smooth flat blades. But here, the impeller is instead covered with pin or needle-like protrusions or even mesh that shreds the air entering, usually through a venturi. Depending on the impeller design you may see names such as needle-wheel, pin-wheel, or mesh-wheel used to describe these skimmers. This is a very popular type of skimmer and likely the most commonly available type today.
Have you ever sprayed a garden hose with a nozzle on it into a bucket of water? You end up with a lot of bubble and turbulence and usually water all over the place. That’s essentially what a spray injection skimmer does, inside a closed chamber of course to avoid the mess. Like downdraft skimmers these too are protected by a patent so only one company makes them.
Additionally, there are a few different ways a protein skimmer may attach to your system. Some are designed to hang over the back of the tank (often known as hang on back or HOB skimmers), while others are designed to sit partially submerged in the sump, and still others that stand completely separate with water supplied via pipes or tubing. In general, skimmers designed for smaller tanks tend to be HOB or in sump models, while stand alone units are designed for larger setups.
Picking a Skimmer
So the big question is which one should you get? Well, there isn’t really a “best” type of skimmer. When picking out one for your tank likely the biggest factor will be finding one that fits your needs. The first thing you’ll need to figure out is where the skimmer is going to be located and then measure to see just how much room you have to work with. If space is tight then that could narrow your options down quite a bit right off the bat. Then when looking at your possible options, in addition to any size constraints, you’ll need to look at the recommended tank size. There’s no formal standard to this rating so you basically have to take the manufacturer’s word for it. However, it’s generally recommended to get the biggest skimmer the available room allows for. The bigger the unit the more effective it will be at clearing the water of waste before it has a chance to break down.
A good protein skimmer is absolutely the best way to remove the bulk of the waste from a marine aquarium’s water. As long as it’s properly maintained it will pull cup after cup of sludge from the water without the need for filter pads or any sort of media. And unlike mechanical filters the waste is completely removed instead of sitting in the media where it can still break down and be released, causing degradation of the water and necessitating more water changes. A protein skimmer really is an essential piece of equipment that should be included in every saltwater aquarium setup.