For marine or saltwater aquarium tanks, protein skimmers (also known as foam fractionating) is important to your marine or saltwater aquarium health. A protein skimmer will remove organic material (like excess food particles or feces) before it breaks down into ammonia and interrupt the nitrogen cycle. It also can remove trace minerals like copper, which is lethal to most invertebrates.
All protein skimmers work on the same principle but the designs vary widely (and the cost as well). Bubbles are blown through the water and organic material attaches itself to the surface through surface tension. At the surface, the organic material is collected or “skimmed” into a cup and you dispose of the contents.
One factor in protein skimmer effectiveness is the ‘dwell time’. It basically measures how long a bubble is in contact with the water. The longer the dwell time, the more chance organic particles have to attach to the bubble.
Another way is to decrease the size of the bubbles. This produces more bubbles per cubic inch and produces more surface area.
Because of the size requirements, a lot of protein skimmers are kept in the aquarium stand but some of the smaller units are hung in the back.
Protein skimmers are more important for fish-only tanks than reef aquariums. A reef aquarium has coral, live plants, and invertebrates that process nitrates whereas a fish-only tank does not.
Co-Current Protein Skimmer
Water is pumped through a plastic column. Air is pumped to the bottom of the column and is commonly expelled through an air stone (a piece of limestone or wood that produces tiny bubbles).
As the bubble reaches the surface, it bursts and releases the organics. As the organics collect, it foams and the foam is skimmed into a collection cup for disposal.
The water enters the column from the bottom, runs parallel to the bubbles, and exits at the top either back into the aquarium or to another filtration system.
Ideally, the column should be milky white with bubbles but as the salts and other minerals clog the air stone, they need to be replaced periodically.
This is the simplest and earliest design (and the least expensive). It’s usually anywhere from 6′ to 18′ and can be mounted behind the aquarium. It’s also great for tanks 30 gallons and below.
Counter-Current Protein Skimmer
This design is exactly the same as the co-current protein skimmer except the water enters at the top of the column, runs against the path of the bubbles, and exits at the bottom of the column.
By running against the direction of bubbles, it increases the dwell time and increases effectiveness, without increasing the size of the unit.
This desing probably has the greatest variance in design. It can be small enough to hang at the back of the aquarium tank or large enough that it needs to be kept below in the aquarium stand. It’s appropriate for tanks from 30-75 gallons.
This is the hobbyist-grade protein skimmer and will meet the needs of most people.
Venturi Protein Skimmer
The venturi protein skimmer depends on high water flow to create vortexes and eddies in the column of bubbles. This increases the dwell time and the effectiveness of the protein skimmer dramatically.
However, because this type of protein skimmer depends on high water flow, you will need a stronger pump than the other types to produce this flow.
Some design rely on an air stone to produce tiny bubbles. Others run the water horizontally through a nozzle and across an intake valve exposed to air. The high speed of the water naturally draws air in and produces bubbles.
This will be your most expensive option but also your most effective mechanical option.
Now not all protein skimmer will fall neatly into these categories. There’s going to be some crossover and improvements but this should give you a broad overview of what to expect.
Before getting a protein skimmer, decide if you need one. If your nitrate readings are consistenly low (under 10 ppm), you don’t need one. If you see high nitrate readings, take several over a few days to make sure it’s not a temporary spike.
If you decide to purchase a protein skimmer, get the best or biggest you can afford. Like picking a good saltwater aquarium tank, making several upgrades can be expensive.
Also, there are other options to control nitrates like other live rocks or live plants. Keeping mangroves, for example, not only filter unwanted nitrates but phosphates as well. And they due to their root system, they can survive in saltwater.