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Inexpensive Wavemaker Impressions

By Adam Cesnales

The WetWebMedia 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:

Early marine 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.

Things changed 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, that is!

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 frustration.

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.

Wet/dry filters

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.

Undergravel Filters

A very typical undergravel fitler.  Photo Adam Cesnales

Undergravel filters 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 hobbyists.

Live Rock

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.

Protein Skimmers

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.

Sand Beds

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 Cesnales

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 deaths.

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

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 some aquarists.

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.


Unfortunately, many 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 and 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.

WWM on Marine Filtration

Related Articles: Marine FiltrationCentral Filtration Systems,

Related FAQs: Marine Filtration 1, Marine Filtration 2Marine Filtration 3Marine Filtration 4, Marine Filtration 5, Marine Filtration 6Marine Filtration 7, Marine Filtration 8, Marine Filtration 9, Marine Filtration 11, Marine Filtration 12, & FAQs on Marine Filtration: Designs, Installation, Maintenance, Troubleshooting/Repair, Brands/Manufacturers, DIY, Reef Filtration, Nutrient Control and Export



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