By Adam Cesnales
crew receives a large number of marine aquarium questions daily. Many of
these questions are about filtration. Many more of these questions are
about problems that the aquarist does not realize are largely the result of poor
filtration choices. There are a lot of reasons why these poor choices are
made, but poor information and shortsighted cost-cutting top the list. This
article will look at why live rock and a good skimmer are the foundation of the
best filtration strategies, and how they are the most economical in the long
run. We will also look at why other filtration strategies such as power filters,
wet/dry filters and under-gravel filters usually result in frustration and
increased long-term costs.
There is plenty of
information on WetWebMedia about individual filtration strategies for marine
aquaria. Steve Pro has reviewed some filtration equipment choices in his
“Impressions” column in this magazine. This comparison of these strategies will
assume that the reader is at least familiar with the basics, so readers who new
to the hobby or would like a review might want to take a look at some of these
links by topic:
aquarists struggled with equipment that was designed for freshwater systems and
was ill-suited for marine aquaria. High nitrates and the accumulation of
organic waste isn’t a problem for freshwater aquarists who can do frequent large
water changes. However, the cost of sea salt makes this an unbearable expense
for marine aquarists.
drastically in 1961 when Dr. Lee Chin Eng published his success at keeping
marine fish and corals alive with his "natural system".. Dr. Eng had very
good success at maintaining marine fishes and live corals in systems that
contained only live rock, live sand, bubblers for water movement, and natural
sunlight. Live rock solved many of the problems that borrowed freshwater
techniques could not, and added a great deal of stability to the systems that
use it. Dr. Eng’s system also stressed the importance of strong water
movement and gas exchange to overcome the lower oxygen capacity of saltwater.
Because of the need for large, frequent water changes (Dr. Eng had the wonderful
convenience of walking down to the beach with a bucket!), Dr. Eng's system
didn't really catch on until the late 1970's and early 1980's when protein
skimmers were adopted by German aquarists as a way to help control dissolved
organic wastes. The combination of live rock, strong water movement and
protein skimming became known as the “Berlin System”, and it’s popularity
exploded since it made keeping a wide variety of marine fishes and even corals
alive in captivity.
So why, after all
these years, are novice marine aquarists still struggling with equipment adapted
from freshwater? Mostly because freshwater is still king. The vast
majority of products produced for aquarium use and sold in shops are designed
for freshwater use. Uneducated employees sell these products for marine
use because that is what they stock and what they know. Very few
manufactures and shops truly cater to the marine aquarium market. The
economics are compounded by human nature: We are all generally cheap and
lazy! It is easier to accept poor advice than to educate ourselves, and
cheaper to buy inappropriate equipment. Such shortcuts are easily
rationalized as being “good enough”. Also, it is much easier to
rationalize spending $150 on a fancy, hi-tech canister filter than it is to
spend the same amount on a bunch of live rock.... until one sees the benefits,
Without taking too
much time to digress from the topic at hand, the issue of cost deserves a bit of
discussion. The WWM crew is occasionally criticized for recommending
expensive equipment or for being hard on aquarists who can’t or won’t afford the
money for quality equipment. The fact is that “good things are seldom cheap and
cheap things are seldom good” and “the sweetness of a good deal is usually
quickly replaced by the bitterness of dissatisfaction”. Our number one
priority is the welfare of the animals that are being taken from the wild and
being kept in captivity. There is no question that providing the best care
for these animals is expensive, and while we try to be sensitive to that fact,
we don’t try to sugar-coat it, either. Our second priority is the welfare
of the hobbyist. By recommending an investment in better equipment, we are
not only saving the lives of animals, but saving the aquarist money in the form
of fewer replacement animals and the loss of their investment if they quit in
We will begin our
discussion by covering two filtration systems that had their moments, but whose
moments have largely past. Wet/dry filters and undergravel filters have
been around for quite a while, and before the wide availability of live rock and
protein skimmers, they were the best systems available. These devices
still have their place in some specialized systems, but aren't the best choices
for the typical marine display aquarium. Most well informed aquarists consider
these systems to be out-of-date and less than ideal.
A typical wet/dry. Photo by Robert Fenner
Wet dry filters
(also known as trickle filters) are contained in a sump and consist of
large surface- area media (usually bio-balls), over which tank water flows.
The media is mostly suspended above the water level in the sump so that incoming
water trickles through it forming a film. The high surface area provides
both growth area for beneficial bacteria and for tremendous gas exchange.
Because of their high capacity, wet/dry filters remain useful for very heavily
stocked systems and large commercial systems. The reduction of nitrate to
nitrogen gas requires anoxic conditions. The highly aerated conditions and
they types of substrates in wet/dry filters prevent areas of anoxia from
occurring, so nitrates accumulate. Specialized denitrifying filters exist,
but these add a great deal of cost and complexity. While wet/drys do have
their place, we will soon see that live rock provides more complete filtration
with plenty of capacity for the typical home marine aquarium.
A very typical undergravel fitler. Photo Adam
consist of raised slotted plates that are placed on the bottom of the aquarium
and covered with gravel. Tubes connected to the void space under the
plates are connected to air pumps or powerheads. Water is drawn down
through the gravel across the void space and up the tubes by the pumps.
Undergravel filters perform similarly to wet/dry filters, but because of their
relatively low flow, they are much less efficient. Many marine aquarists
have used UGF’s with good success, but they are limited to modest stocking
levels and since the entire device acts as a mechanical filter, meticulous
maintenance is required to prevent the gravel bed from clogging with detritus.
Because of the very
gentle flow that they create, UGF's do have a place for animals that are very
physically delicate and may be damaged by powerful pumps or high velocity water
flow. However, the care of such animals should be left to advanced
Live rock has
become the foundation for marine aquarium filtration because it serves a variety
of purposes very well. It provides a natural-looking and attractive
substrate for aquascaping, habitat for ornamental animals, habitat for
scavengers (amphipods, worms, tiny Sea Stars, etc.) and substrate for encrusting
organisms that are both attractive and functional. While there is no
direct harm in the use gaudily-colored artificial corals, ceramic ship wrecks
and bubbling toy scuba divers (except perhaps for their insult to good taste.
But hey - to each his own!), they will never match live rock for it’s
diversity of habitat and the resulting diversity of life that it brings.
Some very nice live rock. Notice the living
coral to the upper right. Purple coralline algae makes the rock
quite attractive and all of the surface irregularities provide surface
area and habitat. Photo by James Fatherree
It is estimated
that a typical morsel of food will be eaten 15 times before it has been reduced
to pure waste. All of the amphipods, copepods, tiny Sea Stars and numerous
other creatures that are introduced with live rock and make their homes in it’s
labyrinth all need to eat! Missed food, fish waste and detritus are all
processed naturally as they are eaten by these critters. With reasonable
stocking and feeding levels, this makes mechanical filtration unnecessary or
even undesirable in systems using live rock. This is especially true in
reef tanks where mechanical filtration would remove the detritus and plankton
that act as food items for corals.
The large surface
area of live rock along with the varying oxygen levels in all of its nooks and
crannies provides an outstanding substrate for biological filtration. Live rock
on it’s own is quite capable of eliminating all inorganic nitrogenous wastes
(Ammonia, Nitrite and yes, with reasonable stocking… even Nitrate).
In order to ensure
that live rock stays "live" and functions well, some minimal maintenance must be
carried out and basic care provided. An occasional blast with a turkey
baster or powerhead will ensure that excessive detritus does not accumulate and
clog the pores in the rock. Maintenance of proper pH, Alkalinity and
Calcium (in that order of importance!) will ensure the good health of encrusting
organisms, especially coralline algae. Healthy coralline algae will out
compete nuisance varieties, so this is very important! Aside from these
basics, live rock pretty much takes care of itself.
While live rock is
expensive (“You want how much per pound for rocks?!?!”), it is not that
unreasonable compared to the often inferior choice of a wet/dry or under gravel
filter combined with artificial decorations. Live rock and the entire
ecosystem that comes with it meets almost all of the needs of the typical
filtration needs of the typical marine aquarium.
Notice the dark brown skimmate in the collection cup.
This is just a few days worth of aquarium wastes! The body of this
skimmer is clear, it looks white because of the high density of tiny air
bubbles. Photo by Adam Cesnales
So what happened to
that morsel of food that was mentioned earlier? Once it has been eaten for
the fifteenth time, is it gone? Where did it go? Some of it did get
incorporated into each of the critters that ate it, but each of those critters
produced some waste. Ultimately, what remains is dissolved organic
compounds (DOC’s). While DOC’s are probably not directly
harmful, they can fuel the growth of undesirable bacteria and algae and they
reduce light penetration through the water by coloring it. Fortunately,
many of these DOC’s (usually proteins) have a part of their structure that is
hydrophobic (is repelled by water) and part that is hydrophilic (attracted to
water). This causes these compounds to be attracted to and form films at
any air water interface. By creating a lot of air/water interface in the
form of bubbles in a protein skimmer, these compounds can be concentrated as
they form foam, and removed. Protein skimming has the added benefit
of greatly enhancing gas exchange.
There is a
mind-boggling array of protein skimmer designs and each manufacturer makes
claims as to why theirs is the best. Specific recommendations are beyond
the scope of this article, but online discussion forums offer a great variety of
opinions, as does the article by Steve Pro that is referenced at the beginning
of this article. Here are some general guidelines: The flow rating (in
gallons per hour) of the pump that runs the skimmer should be very roughly in
the range of about five times the tank volume. As a very general rule,
divide manufacturers recommended tank sizes in half (Euro-Reef and Aqua-C tend
to be more reasonable in their recommendations). Last but not least: you
get what you pay for… bargain models are no bargain. They are ineffective
wastes of money.
Dr. Eng's "Natural
System" used sand collected from the nearby Indonesian reefs. Although the
“Berlin system” employed live rock and skimmers for filtration, they generally
did not contain any sand or gravel. Leaving the tank bottom bare allowed
detritus to be easily removed by siphoning during water changes. These
systems worked very well, but often had persistent levels of nitrate. In
an effort to eliminate those last few ppms of nitrate, substrates gained
popularity in the mid 1990’s. Bacteria in the anoxic areas of the sand bed
strip the oxygen from nitrate and release harmless nitrogen gas as a byproduct.
As an added bonus, different substrates support different types of infauna such
as various worms and microcrustaceans. No only do these critters help
process wastes, but they and their larvae provide an excellent source of food
for planktivores and corals.
A typical deep fine sand bed. The bubbles are
nitrogen gas produced during the reduction of nitrate in anoxic zones.
The dark thread like features to the left are algae and the reddish
thread like features in the center are tiny worms. Photo Adam
Sand beds should be
kept lively. A healthy population of critters to process detritus is
critical to their success. Vacuuming of sandbeds is generally ill-advised.
It not only starves the critters in the bed, it likely sucks them away to their
Despite their many
benefits, sand beds require proper design, materials and maintenance to function
properly. Shortcomings in these areas have caused some aquarists to
experience problems with sand beds. Aquarists who appreciate the aesthetic
and functional benefits of sandbeds are urged to diligently research their
choices and resist the naysayers! Properly constructed and maintained
sandbeds can function well for many years.
Power Filters and Canister Filters
There is no better
example of equipment designed for freshwater use, but woefully misused in marine
aquaria than power filters and canister filters. These filters were
designed as less expensive, easier-to-maintain and less complicated replacements
for wet/dry filters. Most succeed very well in this regard, but ultimately
they are subject to the same limitations. They are highly aerobic,
so nitrates are an issue. Also, without very frequent (more than once a
week) cleaning, accumulated wastes break down in the filter, only to be
reintroduced to the system.
Canister filters and power filters are good choices
for freshwater hobbyists, but are problematic for marine hobbyists.
Photos by Steven Pro
Power filters and
canister filters do have some utility in special cases. A cartridge or
insert for one of these filters can be stored in the sump of the display system
where it will stay colonized with bacteria. When the need for a quarantine
or hospital tank arises, the colonized cartridge can be installed in the filter
for an instantly usable temporary system. Generally, the period of
quarantine or treatment is short enough that it ends before problems arise with
the filter. Canister filters are also useful for the specific specialized
filter media (activated carbon for example) since they provide a convenient
container and high flow through the media.
Hopefully, it has
become clear that live rock and it’s attendant infauna is the ideal filtration
methodology for marine aquaria. Unfortunately, there is no such paradigm
for freshwater, so power filters and canister filters are the only choice.
Algal filters have
been rapidly gaining popularity over the last few years. The basic idea
is that growing algae take up nutrients. Harvesting the algae exports the
nutrients from the system. In addition to their nutrient export benefits, algal
filters also make great habitat for microcrustaceans that are swept into the
system to act as food for fish and corals. Another great benefit is that
by lighting algal filters at night when the lights are off in the display,
typical nighttime drops in pH and oxygen levels are ameliorated.
An algae turf scrubber (left). The screens are
on a teeter-tottering tray that intermittently floods and drains the
screens. An overhead light has been removed for the photo. A
macro algae refugium (right). Chaetomorpha and Caulerpa can be
seen in the photo. Photo Adam Cesnales
The two primary
choices of algal filters are macroalgae refugia and algal turf scrubbers.
Macroalgae refugia use large, rapidly growing algae in a separate but connected
tank. As the algae grows to fill the tank, it is occasionally trimmed
back. Turf scrubbers employ specialized systems that use tilt tables or dump
buckets to provide surges of water over screens that are colonized with turf
algae. These algae are intermittently exposed to air which directly aids
their growth and inhibits the growth of undesirable organisms. These algal
turfs are occasionally scraped to harvest the algae. Poorly designed
systems do not allow exposure of the screens to air. This generally leads
to other species out-competing the turfs and overall poor performance.
Such systems contributed to the undeserved bad rap that turf scrubbers have with
Algal filters in
general, but especially turf scrubber systems tend to color the water with
compounds released by the algae. The original turf scrubber systems
developed by Dr. Adey gained a bad reputation because they did not employ
skimmers or carbon to help control these compounds. However, home
aquarists have had great success by combining these strategies and getting the
best of all worlds. As with all filtration methodologies, it is important
to research specific choices carefully and to understand that proper design,
species selection and maintenance are required for success.
new marine aquarists find themselves frustrated and unsuccessful because of
inappropriate filtration techniques. It is easy to understand why we want
to trust that what our local fish store stocks and sells is appropriate for
whatever kind of tank we want to set up but this isn't always the case.
This is not an indictment of local fish stores. It is hard to stay current
with changing trends when you are trying to run a business, and to stay in
business you have to stock the items that sell well. Most local stores
will order what you want, and if they won't, you can find another (better
informed!) store. The best approach is to be an educated hobbyist.
WetWebMedia and sights like
www.reeffrontiers.com are great sources of information. There are a
lot of good books out there, but there are a lot of poor ones as well. The
good ones are well worth the investment.
Live rock and a
quality protein skimmer will usually cost more to establish than other
filtration methods, but when thoughtfully considered the cost difference is
often small. When the modestly higher cost is considered against fewer
livestock losses, greater success in the hobby and greatly reduced frustration,
it becomes clear that it is a bargain.