Everything You Ever Wanted to Know About Protein Skimming But
Were Afraid to Ask
By Jason Kim
Jason is the founder of AquaC. Inc.
From his web site www.proteinskimmer.com
Aquarticles
Protein skimming has rapidly become one of the hottest topics in the marine aquarium
industry. And for good reason, since this method of "filtration" is one of the
easiest, sure-fire ways to promote the health of a saltwater system. Although most would
agree that a protein skimmer, or foam fractioner, is a must-have on any marine tank, there
nevertheless remains a healthy debate over the subtle intricacies of just how to
accomplish the process of skimming. This debate has led to a small amount of confusion
among some beginning aquarists, and even experienced veterans in a few cases.
We at AquaC pride ourselves as the manufacturer of quality products designed to make
the job of an aquarist as easy as possible. Please take a few minutes to read the
following passages - you're certain to walk away with the knowledge you'll need to
purchase the ideal skimmer to fit your needs. Hopefully, you will agree that an AquaC
skimmer can help you capture the beauty of a coral reef.
Protein skimming is nothing new - advanced aquarists and professionals have been using
the technique for decades. Other fields unrelated to the aquarium industry have also used
forms of foam fractionation to separate compounds from liquids. Only in the last few
years, however, has the widescale market for skimmers exploded. New models and methods
seem to pop up with the frequency of political scandals these days. This has led to a
great deal of controversy as to who makes the best skimmer. This is not an easy question
to answer. An aquarist looking for a small unit designed to skim a 15 gallon tank would
not agree that a six foot tall venturi model would be the best choice. On the other hand,
a hobbyist with a 100 gallon reef would hotly argue that this very skimmer is the best
choice! Who is right??
They both are… There is no such thing as the "best" skimmer!
In many ways, protein skimmers are a lot like automobiles. Some people lust after a two
door sportscar, while others might desire a four-wheel drive truck. Although neither
automobile is quantitatively better than the other, each fills the needs of a different
type of driver best. Although you might not realize it, the skimmers on the market today
vary as much as a Toyota Truck and Porsche Boxter do. And, if we carry this car analogy
just a bit farther, there are the Mercedes Benzes of the skimmer world, just as there are
the Ford Pintos (our apologies to the Ford Motor Company).
The first thing to do, then, is to examine the criteria which are important to you. In
most cases, the two most important factors that will be considered are cost and size.
Money doesn't grow on trees, and most people don't want a skimmer which resembles a Giant
Redwood poking out of their living room floor.
The cost issue is a no-brainer - all else being equal, purchase the most inexpensive
skimmer (unless you're Bill Gates, that is…). Another factor to consider are the
ongoing costs. Protein skimmers require pumps, which suck up electricity. Some of the high
performance models sold today use hefty, energy-sucking water pumps, so be sure to
calculate this cost before your purchase. Another ongoing cost might be maintenance
related. Some types of skimmers will require regular, scheduled cleaning and/or
replacement of air stones. There is more on this below… Choosing the right size
skimmer is a bit more complicated, as several factors need to be considered. First of all,
do you have a sump or will the unit hang off the back of the tank? What size skimmer
footprint (including pump) will your sump accommodate? How tall of a skimmer will fit
under your cabinet? Can the skimmer be placed outside of the sump, and if so, is any
special plumbing required? Before purchasing a skimmer, carefully consider these questions
and make the necessary measurements/calculations to help you choose the best model.
Although size doesn't always correlate with performance, a general rule of thumb says that
a larger skimmer will usually outperform a smaller one (Don't worry guys, we're talking
skimmers here…!).
Another note about your budget… A lot of new aquarists will invest $500 on
"entry-level" equipment and then immediately spend $300 on livestock, all within
the first month or two. This has got to be the biggest mistake that nearly all
inexperienced hobbyists make, and it usually ends up costing truckloads of money in the
long run. After working for several years in a tropical fish store, I can't tell you how
many people ended up pawning off their original, shoddy equipment and investing in quality
products. That $100 queen angel you have your eye on might look great, but if you skimp on
your filtration set-up you are effectively playing Pomacanthus Roulette.
So let's say you set your budget at $250 for a skimmer which must be no taller than
twenty inches, the size of your aquarium stand. Remember, most units require occasional
servicing - don't buy a skimmer that will fill the sump like a fitted glove. Now we can
talk about the real nitty gritty…the most complex factor you will be forced to
consider when purchasing a skimmer - THE METHOD. This, unfortunately, is where it gets
tricky!
First of all, no matter where you go, who you talk to, or what you read, you're going
to hear different and possibly contradictory reasons why Brand X is better than Brand Y,
or why Method A is better than Method B. The fact is, there simply is no such thing as a
"best" skimmer. If your budget is $100, ninety percent of the skimmers on the
market aren't even an option! Since nearly every skimmer is best given a different set of
circumstances, there is really no reason to enter a silly debate over brand names. But we
can talk about the meat and potatoes - what should you look for in a protein skimmer.
The skeptical reader will have read the last statement and wondered how a protein
skimmer manufacturer can possibly avoid entering a silly debate regarding brand names.
Well, we are starting to wonder that ourselves! Seriously though, the answer is very
simple. Although the purpose of this document is to demonstrate why AquaC skimmers are
among the best in their class, we hope to accomplish this fact by educating our customers
about the process of protein skimming rather than by simply stating "we are the
best…" High performance protein skimmers are not inexpensive pieces of
equipment, and we want all of our customers to invest in our products for the right
reasons - which will ultimately guarantee everyone's satisfaction. Now let's dig deeper
into the exciting world of protein skimming…
Protein skimmers benefit water quality by facilitating two major processes -
gas exchange and export of organic wastes.
These are both critical to the maintenance of optimum water conditions. The sad truth
is that no captive system can ever truly duplicate the conditions found on a natural coral
reef. Effective protein skimming can, however, bring us very close to this desired goal.
The beneficial gas exchange that goes on inside of a protein skimmer is largely
dissolution of atmospheric oxygen into the aquarium water. Other gases like nitrogen and
hydrogen also play roles here, but we aren't as interested in them. Some evidence even
suggests that ammonia might be "blown-off" into the atmosphere during protein
skimming. It is important to keep dissolved oxygen levels as high as possible, since most
organisms (fish, corals, inverts, etc.) we keep are used to these conditions found in the
wild. Waste removal is accomplished through chemical interactions between charged
particles of air and water, which allows proteins, trace elements, and other compounds to
become attached to air droplets. These protein-laden air droplets then coalesce into a
thick foam which is skimmed off into a collection cup. Those who are interested in the
technical aspects of protein skimming should read Richard Harker's recent article in Marine
Fish and Reef USA, which is an extremely informative document regarding the complex
chemistry of the process. Delbeek and Sprung's The Reef Aquarium is another
source of information regarding the topic.
Although it is certainly important to understand how and why protein skimming works,
the actual physics and chemistry of the process involve some pretty scary equations. Many
of the factors involving effective protein skimming are far from being understood, even to
this day. Luckily, however, the basics are relatively easy to understand…
In short, the four main factors which govern a protein skimmer's effectiveness
are…
1. Bubble size
2. Bubble quantity
3. Overall flow-thru rate
4. Quality of contact time
Pretty simple, right? Well, it gets more complicated…
First let's talk about bubble size. Smaller bubbles are preferred over larger ones
since they offer a larger surface area to volume ratio. Since the nuts and bolts of
protein skimming takes place on the surfaces of air bubbles, our goal is to maximize this
variable by introducing the smallest bubbles possible. Of course, at some point the
bubbles could become so tiny that they would actually stay dissolved in the water and
cease to produce foam. For most purposes, it is nearly impossible to generate bubbles this
small. The same logic follows for bubble quantity -
since larger numbers of bubbles mean increased surface area, we want to inject as many
bubbles, overall, as physically possible. Once again, it would be possible to inject too
many bubbles (imagine a protein skimmer packed so tightly with bubbles that it was almost
"dry". Given the technology available, however, this has yet to become a
realistic problem.
The overall flow-thru rate and quality of contact time are not as clear cut as the
previous two measures. Some have reported that high flow-thru rates (several hundred
gallons per hour) yield the best results. Others argue that a slow, leisurely flow-thru
rate facilitates the best skimming. Most likely, both schools of thought are correct in
their own way. The actual chemistry behind the mechanism of protein skimming tells us
that, in order to remove the maximum amount of waste possible per bubble, we want a very,
very slow flow-thru rate. This makes perfect sense… If the flow-thru rate is slow,
each individual air bubble can react with the water for a longer period of time. Air
bubbles, after all, don't become saturated with proteins immediately. Research suggests,
in fact, that they continue to become coated with organic compounds for up to 12 minutes
(Harker).
The problem, and this is why the "high flow-thru rate" school of thought is
also partially correct, is that aquariums are closed systems which need to be
"cleaned" at an efficient rate of speed. Imagine holding a vacuum cleaner over
the same section of carpet for ten straight years. Sure, that little square of shag might
be extremely clean once you are done, but what about the rest of the house?? Our goal is
not to maximize the amount of protein removed per bubble, but to maximize the amount of
protein removed per unit time. An efficient protein skimmer, then, is one which removes
the largest amount of waste in the shortest time possible. High flow thru-rates are
beneficial because they allow large amounts of the aquarium water to be processed rapidly.
Although less protein is removed per bubble (because the air and water are not being
allowed to react for very long), it is possible to treat the entire tank volume in a short
amount of time. There is probably a middle ground which yields the best results. It is
important to note that both high and low flow-thru rates can and have been used
effectively, and neither method is definitely better than the other. Our own research with
different flow rates and air-injection methods suggest that for larger tanks (100+
gallons), higher flow-thru rates are better suited than slower ones. This might be due to
the added benefit which high flow-thru rates provide; more thoroughly oxygenated water.
The real answer is far from clear, however.
By now you should have a general idea about the main factors which make some skimmers
more effective than others. There still remains one very large problem, however, and that
is the method. Open the latest issue of FAMA and you're bound to see ads for over ten
different skimmer brands. Do they look the same? Heck no! Do they work the same? For the
most part, yes. Every skimmer has its pros and cons, however.
Our market research suggests that there are six main factors which are
important to customers. These are, in no specific order…
Performance
Initial Cost
Ongoing Cost
Maintenance Requirements
Size
Ease of Use
There are basically five different types of protein skimmer. These are:
The Air-Driven Skimmer…
This method of skimming (sometimes referred to as the counter-current method) is probably
the simplest and has been used for decades. A standard air pump pushes air through a
porous block (either made of wood, glass, or ceramic material) which produces fine
bubbles. Usually, a separate water pump is required to provide flow through the skimmer
and back to the aquarium or sump. The main advantages of the air-driven skimmer are its
low initial cost and quality of contact time. Wooden airstones produce tiny, wispy air
bubbles that provide a high air-surface to water ratio. Since flow-thru rates are kept
relatively low in this type of skimmer, bubbles are allowed to react with water for long
periods of time. This is the hallmark of an air-driven skimmer, which feature a high
"protein removed per bubble" ratio. Furthermore, since control of the water
flow-thru and air-flow rate are often independent of each other, they can be manipulated
individually to yield the most efficient skimming possible. Another positive feature of
air-driven skimmers is that the air bubbles are typically allowed to react with the water
for very long amounts of time.
Unfortunately, all skimmers have their drawbacks. Air-driven skimmers are utilized most
efficiently when the flow-thru rate is low - which insures that the contact time between
air bubbles and water is maximized. Although this yields a high "protein removed per
bubble" ratio, the "protein removed per unit time" ratio can actually
suffer as a result. This might be why larger tanks seem to do better with the higher flow
design skimmers. Furthermore, most air pumps available to hobbyists are simply not
powerful enough to deliver tremendous quantities of air to the skimmer. Air-driven protein
skimmers can certainly be utilized efficiently and will produce good results, as long as
we keep these factors in mind. Air-driven skimmers also require regular maintenance - wood
air stones must be replaced relatively often in order to keep the skimmer working
efficiently.
The Venturi Skimmer
The "venturi skimmer" is actually a general term which covers a broad class of
different designs. Most skimmers on the market today utilize the venturi effect in some
form or another. So what is a venturi, anyway?? It's just a high-tech word for a
special-shaped tube which draws in air. A good venturi can introduce fairly large amounts
of air. Venturi skimmers also feature higher flow-thru rates, and require less regular
maintenance, both advantages over the air-driven design. These skimmers are not without
their drawbacks, however. They can be loud (imagine the sound of air being blown through a
small straw), and the venturi opening can clog in a relatively short amount of time, which
adversely affects performance. Most high performance venturi skimmers are either very
expensive or very large, making space and budget considerations a factor.
The Needle-wheel skimmer
This type of skimmer is actually a hybrid, since it uses a venturi to initially introduce
air into the water. Once air is injected into the skimmer, it is drawn through a water
pump with a special impeller designed to chop incoming bubbles into a finer mist. These
needle-wheel impellers can really hack bubbles apart, which is great since small bubbles
are ideal for efficient skimming. The better needle-wheel skimmers on the market are
notorious for building a dense, milky froth. This makes for efficient skimming in a
relatively compact package. As a result, this type of skimmer is extremely popular, with
new designs popping up every month or two. Although the air and water flow rates in these
skimmers are high, they still fall short of the air-induction style skimmer which we will
talk about next.
The Downdraft skimmer
Initially, several different companies manufactured similar versions of the now popular
downdraft-style protein skimmer. Since A.E. Tech owns the patent rights on the design,
most of these companies are no longer competive. There remains one brand which utilizes a
hybrid variation of the venturi and downdraft concepts which also enjoys quite a bit of
success, and does not infringe on A.E. Tech's patent. Downdraft skimmers feature high
flow-thru rates. They also inject large amounts of air into the water. A typical downdraft
skimmer can cycle the entire volume of a 100 gallon system several times an hour. This
makes for excellent oxygenation and ensures that all of the water is treated in a short
amount of time.
Downdraft skimmers are often advertised as being the "best" skimmer on the
market. This, in on our opinion, might be a bit of an overstatement. Although this design
works well, it is not without its disadvantages. These skimmers are notorious for being
large… many models stand several feet tall. They also require a very strong pump to
run correctly, in many cases a pump which is expensive and energy-thirsty.
The Spray Induction skimmer
Perhaps it is not a very catchy title, but this is the name we chose to describe our own
skimmer design. AquaC skimmers work on the very same principles as the others already
described, but they achieve an air-water mix in a very unique way. This new method, which
we call Spray Induction, makes for very efficient skimming in a compact package.
Remember the six main factors to consider when buying a skimmer? These were
performance, initial cost, ongoing cost, maintenance requirements, size, and ease of use.
After testing nearly every other type of skimmer on the market, we have found that the
Spray Induction design yields excellent results when all six of these factors are
considered. This design seems to inject the largest amount of air for a given pump size,
and it is extremely short and compact. There are virtually no maintenance requirements or
parts to replace. Once broken in, this type of skimmer is truly a "set and
forget" piece of equipment.
In fact, we've developed a company philosophy based on the idea that customers want the
best bang for their buck.
Now that you understand which qualities to look for in a skimmer, you should be able to
scrutinize the different brands and find the model that best suits your needs… Decide
which criteria are most important tp you.
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