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Power Filters

How they work and what to look for.

By Richard Thompson |

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Those of us who have been in the hobby quite a while have seen the power filter evolve from its humble ancestor, the corner box filter, into a wide variety of sizes, shapes and configurations. If you ask experienced, long-time hobbyists what they remember about early power filters, they will likely tell you how many designs have come and gone, and come back again.

Some overflow power filters have remained with us through the recent decades. Older hobbyists will remark on the Supreme line of filters, which is still alive and well, even though the popularity of these units dates from the early 60s.

Then there was the advent of what was a "revolutionary" idea in filter design when the Metaframe Corporation unleashed the Dynaflo Motor Filter in the mid-1960s. These filters used a magnetic drive impeller and motor that offered high flow rates. The motor was located at the bottom of the filter box in a plastic case to deter rusting. It was at this point in the hobby that power filters became very popular (along with undergravel filters). The name Dynaflo became the name in power filters.

But the Dynaflo wasn't without serious competition. In 1970, the Biozonics Corporation introduced their version of the overflow power filter — the Biozonics 3-Stage Power Filter. This power filter utilized a foam block, a bag of activated charcoal and a pre-filter siphon bag as its media. The magnet drive impeller had to draw the water all the way through the media in order to pump it out and back to the aquarium. Sound familiar? Well, it turns out that this filter design was the forerunner to the AquaClear filters manufactured by Hagen. In fact, the Biozonics 3-Stage Filter eventually became the Hagen 3-Stage Filter before the introduction of the AquaClear.

In 1975, Metaframe/Living World introduced a new version of the Dynaflo, one that utilized a filter cartridge. This cartridge was not too different from current cartridges in that it was made up of a plastic frame with two sides of woven polyester. Inside the cartridge was a pre-measured amount of charcoal or carbon. The cartridge made media changes extremely easy by eliminating the need to dig out all of the wool and charcoal hobbyists used to stuff into filter boxes.

From this point on, many manufacturers were trying to outdo each other. Aqualogy and Cosmic Filters were up against Supreme and Dynaflo (in its many forms), which were pitted against the Hagen 3-Stage, and so on. From the late 1970s to the early 1980s, the hobby witnessed additional overflow power filter innovations, such as the Whisper Power Filters, Marineland Auto-Flo and Penguin filters, and new generations of the AquaClear and redesigned Dynaflo. The most recent evolution is the Bio-Wheel, which is a variation on the basic power filter design.

For many of the beginners reading this, it may not mean much, but for the aquarists who have been around to see the process occur, they witnessed the full evolution of what is available in overflow power filters today. They have also been through the good and the bad, dealing with manufacturers' attempts to "build the better mousetrap."

The Overflow Power Filter
The overflow power filter may be the most commonly used filter in aquariums today. These filters are all basically designed to perform the same function. The idea is to draw aquarium water into an intake stem by the suction created with the filter impeller. The impeller, powered by a small motor, spins water into the adjoining filter box, which is filled with media dictated by the filter's design. The water then travels up through the media and overflows through the output area at the top of the filter box, where it returns to the aquarium and is circulated.

Seems simple enough, doesn't it? Well, as a matter of fact, when looked at from the simple description given above, it is. But this is not actually the case, as we shall see. Filters using this design concept are indeed very popular, and most people who own them find these filters to be fairly trouble-free, easy to maintain and clean, and inexpensive to operate.

But there are questions. Do they all really operate efficiently? Or more appropriately: If it says "filter" on the box, does it truly filter the way overflow filters are designed to work? Perhaps the best way to find the answers is to make your own observations and determine for yourself whether the filter is doing what is should for your aquarium. Below are some things you can do yourself and ideas to consider.

First, notice the design of the filter box. Looking at the design of the box can tell you a great deal about where the water will travel within it after the water is expelled by the impeller. The impeller cover (if the filter has one) needs to be considered along with this because the cover will affect the direction of water flow inside the box.

Second, to determine how well water is passing from the bottom to the top of the media, place some carbon grains at the bottom of the filter box. By noting the path they take, you will be able to see what water movement there is and whether the filter is truly using the media to its utmost efficiency.

One very important point to remember is that the media each manufacturer produces for its filters are designed the way they are for a reason. These designs are the result of testing to ensure that the filters operate efficiently while providing optimal performance. Replacement media for these filters from other companies may or may not take into consideration the configuration, flow rates, flow patterns and specifications of the filters.

A good rule of thumb is to use the original manufacturer's media unless you are convinced that the replacement media from another company really is correctly designed for your filter. The one exception to this may be the amount of granular activated carbon in some cartridges. If the cartridge does not fill the space intended for it in the filter box, water — which will take the route of least resistance — will flow around instead of through the cartridge. Therefore, it may be necessary to open the top of the cartridge and add more carbon, thus creating a tighter fit and forcing the water through the cartridge, where it will come in contact with the carbon. The additional advantage of more carbon is that it increases the amount available to remove dissolved chemicals in the water.

What Makes It Work
The heart of any power filter is the motor and impeller. One of the most trustworthy motor designs on the market today is the epoxy-filled motor with an impeller well into which the impeller is placed. The motor consists of a coil of wire (varying in size depending upon the technology available) that is surrounded by epoxy to seal the coil from dust, water and humidity. Some motors have Underwriter's Laboratory (UL) approval, which means that the cord and plug have passed specific tests and standards.

Impellers in power filters generally consist of a magnetic cylinder and a plastic top with fins similar to a fan blade. As the magnetic field in the motor changes in polarity, the polarities of the coil and the permanent magnet (the impeller) are changed at the same time. Basically, one pole of the coil is designated as north pole and the permanent magnetic is also designated north. When this happens, the poles repel each other and the impeller begins to turn. When the poles subsequently change to south, they also repel and the impeller turns some more. As the polarity rapidly changes from north to south and back again, the impeller turns inside the well of the motor.

The rate of water flow depends on the size of the fin blades and how many fins there are on the impeller. If you were to take apart the motor units of a power filter that pumps 100 gallons per hour and one that pumps 300 gallons per hour, you would see that the number and size of the fins on the 100-gallon impeller would be fewer and smaller than on the 300-gallon impeller.

Another aspect to consider when looking at motor and impeller design is the wearing properties of the impeller shaft. Most power filters incorporate a metal shaft as part of the impeller unit. This shaft is placed through the center of the impeller and is attached to the motor housing by rubber end caps at each end of the shaft. Sometimes, washers made of nylon are placed between the end cap and the impeller unit to cut down on wear and noise. If this complete unit is anchored solidly in the impeller well and at the top, the impeller will center correctly and run smoothly and quietly. In some cases, the impeller is never truly centered inside the motor and will cause unnecessary and serious wear on the shaft. At that point, the impeller unit will begin to wobble on the worn shaft and will become noisy.

One interesting design allows the impeller unit to spin freely on an anchored shaft inside the motor unit. The magnetic force lines within the well center the impeller unit automatically, reducing the incidence of wear, noise and friction created by the impeller.

Make sure the motor of the filter that you are considering purchasing has a self-cleaning feature. This consists of a small cavity that has been cut into the impeller well so that silt, debris and some amount of protein deposits coming off the impeller as it spins will be rinsed out of the impeller housing. Even though it is recommended that any deposits found on the impeller be removed on a regular basis, the self-cleaning feature will reduce the possibility of impeller jamming while the filter is in operation.

Water Return
All of the overflow filters on the market return water to the aquarium by the means of an output "director." The type of water return flow (waterfall, etc.) depends on the design of the director. An extremely important design element to look for in an output director is that it delivers water back to the aquarium as far as possible from the intake stem. The goal is for the filter to process unfiltered water, not water coming from the filter itself.

Another consideration of particular importance when examining output director design is sufficient surface agitation. It is at the surface of the water where oxygen is acquired and carbon dioxide is released. A smooth water surface limits the exchange of these gases. High levels of dissolved oxygen and low levels of carbon dioxide are important to the health of your fish (although for live aquatic plants higher levels of carbon dioxide are desirable).

The store where you purchase your filter should have a working model that will allow you to see how effectively the surface is agitated. Make sure that the water flow from the filter breaks the surface tension of the water. The more water molecules that come in contact with the oxygen in the air, the more oxygen will be absorbed by the water. An output director can also increase filter efficiency if the flow is strong enough to create currents in the aquarium water, thus keeping particulate matter suspended long enough to be removed by the filter.

Categories of Filtration
There are three types of filtration required for a healthy aquarium: mechanical, biological and chemical. A power filter will incorporate one or more of these three categories of filtration depending on the design and how the hobbyist sets up the filter.

Mechanical filtration is simply the physical removal of solid waste matter (food particles, feces, dead aquatic plant matter) from the water. The basic goal of mechanical filtration is to remove particulate matter before it decays and degrades the water quality. Mechanical filtering media includes foam sleeves and blocks, polyester fibers, diatom powder or specially designed sleeves known as "micron sleeves." For general use, foam or polyester works quite well. The other materials clog easily and are only used periodically to "polish" the water.

Biological filtration is the process by which organic wastes are broken down and converted to less harmful compounds via aerobic bacterial action. These organic wastes, which are produced by fish metabolism and respiration and decaying fish food, release ammonia into the water. Ammonia is highly toxic to fish. It is converted by one species of bacteria into nitrite. Nitrite, although less poisonous than ammonia, is also lethal to fish. Another species of bacteria converts the nitrite to relatively non-toxic nitrate. Once the nitrogen cycle is up and running, nitrite tends to be more of a problem than ammonia if there are too many fish or they are overfed. Nitrate does accumulate in the water but can be removed through regular water changes.

These nitrifying bacteria are usually found in the media of the filter as long as there is a strong flow of oxygen-rich water. The key to effective biological filtration in a power filter is simple. The more media volume there is in the filter, the larger the colonies of bacteria and thus the more effective the nitrifying activity.

Chemical filtration refers to how granular activated carbon, resins and ion exchange products can control dissolved waste products in the water, as well as change the characteristics of the water quality. Depending on the media used in the filter, any power filter can be an efficient chemical filter if it is properly maintained by the hobbyist.

Flow Rates
Depending upon the configuration of the impeller fins and the size of the filter box, overflow filters will have flow rates that range from 100 gallons per hour to more than 500 gallons per hour. When choosing a filter for an aquarium, keep in mind that it must have sufficient capacity for the aquarium it is on. A general rule is that the filter should be able to process the volume of water in anaquarium a minimum of four times each hour, although this rate tends to be lower for larger aquariums (55 gallons and greater.

The listed flow rates for filters are generally determined without any media in the units. Thus, the addition of filtering media will reduce the actual flow rate by as much as one-third. As the media become clogged, the flow will be reduced even more. Regular filter maintenance is therefore critical to effective filter performance.

The three categories of filtration listed above are all affected by flow rates. In terms of mechanical filtration, the higher the flow rate the better. On the other hand, biological and chemical filtration require that the water be in contact with the media for at least a minimum amount of time, so an extremely rapid flow of water is of no benefit.

For a 10-gallon aquarium, a filter rated at 100 gallons per hour is more than adequate. A 50-gallon aquarium will operate well with a filter capable of processing 300 gallons per hour. Very large aquariums may require the use of two filters in order to achieve sufficient turnover rates.

Flow controls are available on most power filters, and can be a useful feature. Although one of the reasons for having an efficient power filter on an aquarium is to remove particulate matter, this can become a liability when feeding the fish. With a flow control, you can adjust the flow rate downward to reduce the likelihood of fish food being collected by the filter. This will prevent the media from clogging rapidly and will also reduce the amount of fish food lost to the filter. The other reason why a flow control can be beneficial is that some species of fish do not like turbulent water or strong currents. Being able to lower the flow rate, particularly if the filter is somewhat large for the size aquarium it is on, will eliminate this problem.

Other Factors
Warranties on power filters can also be important when choosing which filter to purchase. If you are one of those people who seem to experience the bad luck of having items break immediately after the warranty period is up, you may consider a warranty to be a major factor in your purchasing decision. Most manufacturers currently offer a 90-day warranty on their filters, although some offer warranties of up to two years. Usually the warranty applies to only the motor unit. Most manufacturers, however, will stand behind the filter even after the warranty period is over.

Some manufacturers offer free media with the purchase of their filters. Although media are not a major expense, it is nice if you don't have to spend additional money just to get the filter up and running.

Power filters represent one of the more expensive pieces of equipment when setting up an aquarium, and a hobbyist should have as much information as possible when choosing one. Making the right selection is important not only for the peace of mind of the aquarist, but also for the health of the fish.

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A    C, VA

1/17/2011 11:30:41 AM

thanks for the info

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