Marine (Saltwater) Aquarium Protein Skimmers
Sections include:
*Basics (Overview)
*Types of skimmers from air driven, Venturi, Aspirating; Needle Wheel, Downdraft, Spray Injection, to combinations.
*Troubleshooting
*Summary

Updated 5/26/09

Information and opinions here are not only based on my experience in the Aquarium Maintenance business (over 30 years) but also of other colleagues in the higher end aquarium maintenance and design business I know and speak to generally on a monthly basis.
I will also add as pointed out to me by a respected member of Everything Aquatic Forum that Marine Protein Skimmers are a fast growing technology area of aquarium keeping, so as in lighting, UV Sterilization, Redox, etc., what may be true today may not be a year from now. I can vouch for this even as to my own opinions as to the use of Protein Skimmers, and that is 20 years ago I found the benefits of often finicky and unreliable protein skimmers often not worth the trouble as per the payoff in results when compared to other filtration methods (especially since I could only visit a client once per week). However, as of the last decade I have to admit a reversal of opinion, and this opinion is based on controlled tests as well and that is the much improved protein skimmers of today are much more reliable and effective and are worth the expense and any extra hassles.

Basics
A protein skimmer is a filtration device used in marine tanks (they do not work in freshwater) which employ a chamber with a column of fine bubbles. Surface tension attracts organic waste to the bubbles & carries it through the column (called foam fractionation); then it is "skimmed" into a collection cup. This process Protein skimmers use to remove nitrogenous wastes (protein based organic waste) is also called foam refraction. The protein skimmer collects this waste in a cup, where it is then emptied (either by hand or a drain as in larger “Pro” models).
Protein Skimmers come in pump driven and air driven models. Within the pump driven there are different types: Venturi, Aspirating, Downdraft, and spray injection; the first two being most common.
Protein skimmers generally only work in marine aquariums where they are very popular in reef aquaria, as they are often needed to keep nitrates below .20 ppm for the delicate marine invertebrates.

The advantages are that they remove nitrogenous waste before they can go thru the nitrogen cycle and become nitrates. The disadvantages are some are messy, take frequent adjustments (at least on many commercial models), and in my experience, over rated especially for marine fish aquariums. I also have kept many reef aquariums successfully with and without protein skimmers although I do recommend protein skimmers for reef aquariums (especially as of late with the much better skimmers now available).
However what I personally find interesting is that many of the aquarists that swear by protein skimmers totally trash UV Sterilizers, yet I have found from experience (I had to service what I sell, and if I sold trash, I had to service trash!) that often UV sterilizers had a more positive attributes than the older protein skimmers (I would not apply this analogy to the high end modern skimmers). That said, a good Protein skimmer is a useful tool in marine aquariums especially when used in conjunction with the Berlin Filter Method for reef aquaria and should be considered, more so if you are planning on keeping delicate corals!

Air Driven
The co-current air driven models (also called columnar skimmers) are the most basic although not always the simplest to use as these cheap Skimmers are often temperamental to water levels in the tank and the limewood air stones used by these skimmers clog frequently. However these can be an inexpensive entry level Skimmer for 10 -60 gallon marine aquariums.
Personally these skimmers can often be more trouble than they are worth, so I would strongly recommend one of higher end skimmers recommended further in this article.

Venturi
Of the pump driven Skimmers, the co-current Venturi models are the most common and popular. This style uses a water venturi pump (sometimes referred to as an aspirator) which is used to introduce the bubbles into the water stream. The tank water is pumped through the venturi, in which fine bubbles of the correct size and number are introduced then enters the skimmer body.

The Venturi Skimmer design lends itself to basic low end protein skimmers that although certainly are not the best, these will still allow for reasonable protein skimming for a lower price for marine keepers not keeping high end marine life and on a budget. However the higher end Venturi Skimmers such as the V2 will far surpass the lower end venture skimmers (such as a Rio Nano Skimmer), due to much better time, bubble exposure time in the current, and its bubble stop that allows for bubble recycling.

As well, not all higher end venturi skimmers are equal, some of the more basic designs such as the Bak Pak work well, but the newer designs such as the V2 Skim by Tropic Marine also has a patented Bubble Stop in which the skimmer is fed 'dirty' water from the aquarium as a means to re-circulate water within the skimmer multiple times before it is returned to the sump or the aquarium.
The Tropic Marine V2 Skim is one of the better ones with the latest in venture skimmer technology. This skimmer has a venturi injection system which optimizes the perfect mixture of fine air bubbles and water and ensures intensive, efficient skimming and the removal of proteins and other harmful toxins (waste) from the aquarium. This Skimmer also has a Bubble stop feature that essentially re-skims the water as well as prevents bubbles/foam from re-entering the aquarium.
Each time water is re-circulated within the skimmer any air bubbles in that water sample are destroyed and new bubbles are generated by the re-circulating pump venturi apparatus so the air-water contact time begins again for these newly created bubbles.
For the money, the V2 Skim the best Protein Skimmer you can buy unless you are willing to spend more money for the even more advanced mesh wheel skimmers such as the Warner Marine, ASM skimmer, or similar for what is often amore temperamental skimmer.

Aspirating; Needle Wheel/ Mesh Wheel
An aspirating or mesh wheel Protein Skimmer generally uses an impeller which consists of a mesh material that is attached to a plate or central axis on the rotor. The purpose of these modified impellers is to chop the air that is introduced via a venturi apparatus or external air pump into large amounts very fine bubbles. Another advantage of this style when done correctly is that these skimmers generally have a larger neck size that allows for less clogging of bubbles/foam, this is due to generally higher bubble production that allows for a wider neck (although my personal opinion and that of many others in the business is that one should be cleaning the neck each time one empties the foam cup as the cup generally fills in most skimmers long before this becomes a real issue).

This style (such as used in a model by Coralife which I do not recommend) is gaining popularity; however this style still has some bugs in that not all of the impellers used by these always chop the air bubbles properly due to anomalies in the flow and impeller design that can result in pump burn up. Part of the problem with this style skimmer is that it does NOT lend itself to cheap low cost designs and is temperamental.
However as of this latest re-write (update) of this article, many premium mesh wheel skimmers are being made at a lower cost (although still at a higher price than high end venture skimmers such as the V2 Skim). I will also admit that at this point in time I am mostly relying on feedback of colleagues in the higher end aquarium maintenance and design business in LA since I am not currently able to run controlled tests on these skimmers.

The ASM Protein Skimmer is one of skimmers in this category that I can recommend based on the high end marine aquarists that use it. What differentiates this aspirating skimmer from the rest is that has a unique "custom" impeller housed in the specifically modified Power Head that chops the bubbles very finely. Another aspect of this aspirating skimmer is that it combines a venturi with its custom meshing needle wheel pump. The negative to the ASM Protein Skimmers is the price, as these units will retail for many $100s of dollars. I will also add as of this latest update, that I have been told via a respected member of Everything Aquatic that this skimmer has some issues with the mesh wheel pump, although this has not been confirmed by others in the aquarium maintenance and design business as of this latest update.

Other high end skimmers in this category include the Warner Marine Skimmer and the brand new Via Aqua Needle Wheel Protein Skimmer.
I currently do not have much feedback from reliable resources on either of these skimmers (although the Warner Marine does come from one trusted source).
The Via Aqua Needle Wheel appears to have a good design and my experience with 80% of their products is usually exceptional, especially for the price/value (but then there is there is the 20% of products that have not performed as expected).
(Pictures can be clicked to enlarge)

Downdraft
A downdraft protein skimmer injects water under high pressure into tubes that have a foam or bubble generating mechanism then carry the air/water mixture down into the skimmer and into a separate chamber. This design is generally used in large aquarium systems uses tubes with plastic media (often bio balls) inside to mix water under high pressure and air in the body of the skimmer resulting in foam that collects protein waste in a large collection cup.

Spray Injection
The Spray injection skimmer (such as the Remora, are a take off from the Downdraft Skimmers) uses a pump to power a spray nozzle, set a few inches above the water level. The spray action entraps and shreds the air into very fine bubbles in the base of the unit, which then rises to the collection chamber.

The Spray Injection Skimmer is a fancy new name for the Downdraft style Skimmers which work well in the large industrial size environment in which they were originally designed for, however this design does not lend itself to small sizes well.
This style skimmer also can clog with time; also one of the more popular models of this style is sensitive to water levels, tends to produce a watery muck (instead of foam), and can be temperamental when used in a sump environment.

These skimmers are really being hyped and over promoted, but personally I would recommend steering clear of these units, not that they cannot work, however for the same price a V2 Skim will far out perform it and for far less money you could probably do just about as well with a Rio Nano Skimmer or a Via Aqua Multi Skimmer

Basic Skimmers, (Skimmer filter combinations)
A couple of basic skimmers for beginners; Via Aqua Multi Skimmer with small to medium aquariums is relatively simple, with a mechanical filter cartridge, bio filtration ability, and most of all the Multi Filter has a built in UV Sterilizer combination.

For a really simple protein skimmer for a Nano tank I recommend the Rio Nano Skimmer.

Protein Skimmer Troubleshooting

*Collection Cup filling with water:
• Water level too high in skimmer, adjust skimmer upward in sump, tank, or in HOB applications
• Check water outlet (or water outlet valve if your Skimmer is so equipped); make sure there is proper flow.
• Check bubbles; make sure you have adequate fine mist bubbles.
*For air driven Protein Skimmers make sure you can blow through the wooden air stone relatively easily, otherwise replace. Check the air pump as well.
*For Venturi Skimmers, make sure your venture is adjusted properly, with the air intake facing outward in some protein skimmers when inserted into the pump exhaust nozzle. Make sure that the pump itself is properly drawing and expelling water.
*For Needle Wheel, check pump flow as with the venture, as well check the impeller that “chops” the air bubbles for damage or impediments.

*No foam in the Collection Cup
• This is normal for a new skimmer set up. The proper dry foam that is needed to collect the protein in the salt water, will take approximately 12 to 34 hours to start skimming. In new tanks, with little or no bio load, this may even take a few weeks.
• If there is adequate bio load and salinity, you may have to make very minor adjustments in skimmer height, relative to water level and make adjustments to venturi inlet.
These adjustments need to be very minute, often Protein Skimmers require patience and constant adjustments, especially the more basic models.
• If powerhead driving a Venturi protein skimmer is too deep in the water, an insufficient amount of fine bubbles will be generated. The powerhead should be as close to the surface as possible, as increased depth will affect the ability of the Venturi to draw in air, reducing the skimming efficiency.
• A good counter current is important as well as this is in part how Protein skimmers work is a fine mist of bubbles against a counter current of water.
The larger the reaction chamber for bubbles to interact with the counter current, the better your dry foam production, which is why I do NOT recommend the unfortunately popular Spray Inject Skimmers that are quite over priced for what you really get.

*Bubbles are escaping the Skimmer into the tank
• Often this is caused by chemicals that have been added which result in increased surface tension of the water. Stress coats, de-chlorinators, medications, and water conditioners (which are present in most synthetic salt mixes) are just some of the additives that will cause this to happen. Carbon will help to remove the compounds that cause this problem, as well many of the better high end Protein Skimmers have “Bubble Stops” to prevent this and recycle these bubbles such as the Tropic Marin V2 Skimmers


Conclusion

Here are some important aspects to consider so as to a purchase a skimmer that performs correctly:
• Contact time of bubbles and water inside the chamber (the longer the reaction chamber, the better in most cases)
• The size and consistency of the bubbles produced (very fine bubbles are best)
• The relative volume of bubbles produced
• The ratio of air to water
• And the turbulence or friction inside the reaction chamber which may cause poor efficiency in some poorly designed units.
• The neck size is important as well, a smaller neck (which is to allow for lower bubble production), can clog easier and may need to be cleaned more frequently.

Please beware of claims of some high priced skimmers such as Spray Injection models as these units do not have the contact time (due to short/small reaction chamber) to maximize protein refraction. Although units such as these due have excellent size and volume of bubbles, the small size of the reaction chamber minimizes effectiveness so that one of these units may perform better than similar size entry level skimmers such as the air driven Lee’s or the Rio Nano/Via Aqua Multi Skimmers venture skimmers; the price at nearly $200 is nowhere near the increase in effectiveness over a Rio Nano Skimmer (or similar) that costs under $30 as a price vs. increase in effectiveness comparison.

Finally, consider how much you can afford and your time as well. Obviously if you plan to keep SPS corals, I would consider a premium Protein skimmer a must, however even here, your time needs to be considered. For example, the mesh/needle wheel skimmers tend to be on the cutting edge of marine protein skimming, HOWEVER the issues of pump burn out and the temperamental nature of these skimmers may make these a lesser choice for many. I personally still find the advanced venturi V2 Skim an excellent choice when these potential issues are considered (as well as price, but this is already becoming less of an issue).