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Canister Filter Impressions

Canister Filters

By Steven Pro

A lush freshwater planted tank filtered exclusively with a Fluval Canister filter.

Canister filters are an often maligned piece of equipment in marine keeping, yet they are a staple in the freshwater portion of this hobby.  This is because with most saltwater setups the primary means of biological filtration is carried out by the live rock, sand, or algal components in a refugium.  In these instances, one does not need or desire the additional filtration of a canister, and the money saved can be put into a top notch protein skimmer.  In freshwater setups, canister filters are utilized a great deal because they can provide the hobbyist with mechanical, biological, and chemical filtration all in a compact package.  Plus, many of the better units do this in an inconspicuous way by running quietly under the tank in the stand almost completely out of view.  This is in contrast to the undergravel filters with their noisy airlifts or unsightly powerheads in the tank combined with hang-on the back power filters.  While this combination of filtration works well, if one wants a clean look to their tank and does not want to see a lot of equipment, a good canister filter is a better choice

Hagen Fluval 3-Series (103, 203, 303, & 403’s)

Canister filters fit neatly under the aquarium stand.

While these models are no longer available, having been supplanted by the 4-series units, I wanted to take a moment to discuss them because I actually preferred the older type to their newer brethren.  In detailing what I liked about these versions, I hope to illustrate specifically why I don’t care for the new line and what I wish had not been changed.

The 3-series came with several interlocking baskets, which allowed the aquarist to use whatever combination of filter media that was needed.  This provided a great deal of flexibility to put together a filter that combined the exact aspects and amounts of biological, chemical, and mechanical filtration that the aquarist desired.  If sufficient biological and mechanical filtration was carried out by other means, these canisters could be packed strictly with various types of chemical media like activated carbon or special resins for absorbing phosphates, nitrates, or anything else.  And of course, the opposite was true. The filter baskets could be filled with mechanical or biological media or any combination of these.  They were truly a versatile workhorse.  As a standard offering, the bottom basket came with ceramic noodles that functioned as a biological filter, but would also break up larger pieces of debris.  I would usually fill the middle basket with chemical media like activated carbon, Boyd’s ChemiPure, or Poly-Bio-Marine’s Polyfilter.  The top chamber came with a large foam block.  This had the dual purpose of mechanical filtration of particles and biological filtration as it colonized with beneficial bacteria.  Later models came with this sponge sliced in half so you could alternate cleaning or replacing the foam so as to maintain a healthy population of bacteria.

This series did have a few problems.  One, there was not a good way of disconnecting the feed and return hoses from the filter body for maintenance.  Also, there was no good way of purging the filter of air when it was reattached to the hoses.  The user just had to hope there was enough water in the hoses to start a siphon and to fill the filter with water.  At some point, Hagen began adding a ball syringe (similar to what one uses to clear mucus from a baby’s airway) for use to clear the tubing of air.  These worked ok, but it was an added piece of equipment to keep track of and if the tubing had completely lost its water, the user had to pump the ball thing like crazy.  All in all though, these were a workable design and could be counted on for good performance with a moderate amount of maintenance.

Hagen Fluval 4-Series (104, 204, 304, & 404’s)

The Fluval Series

The 4-series is supposed to be the ‘New & Improved’ version of Hagen’s Fluval canister filters, but to be frank, I don’t like them as much as the older design.  The ‘dirty’ water must first pass through a sponge block which clogs easily and requires frequent cleaning or replacement.  This is a big negative in my mind for a canister filter.  Since canister filters are inherently more difficult to clean than comparable hang-on power filters, a high maintenance canister is a big drawback.

On the other hand, the 4-series models do have several pluses.  After the sponge filter section, the water passes through a series of baskets which can be filled as the aquarist desires, which is a nice attribute.  Also, the hoses on the 4-series come with a quick disconnect feature that incorporates a check valve in the hoses to eliminate the loss of water and the subsequent mess on the floor.  Lastly, they have a built-in primer to manually pump water out of the tank to fill the canister filter with water after cleaning.

Being an aquarium maintenance guy, I really dislike the new design with the water first passing through the sponge filter.  This makes for much more frequent cleanings than the older design.  Because of this design flaw, I am reluctant to recommend this brand anymore.

Marineland H.O.T. Magnum

H.O.T. Magnum Filter.  The picture on the package shows the pleated filter option installed.

The H.O.T. (which is an acronym for Hang-On Tank) Magnum is a very nice overall design similar in many operational respects to the multitude of hang on power filters that I reviewed in my July/August Impressions column.  These incorporate a pressurized canister filter in a hang-on design, but as with many of the hang-on power filters, they are too small to be as versatile as the larger under tank canister filters in this category.

These filters come standard with two different filtration packages (only one can be used at a time).  The first package is a basket which can hold activated carbon or any loose filtration media.  This basket is then enclosed in a bonded fiber pad for mechanical filtration. The basket could be loaded with biological or chemical media, but I prefer to load it only with activated carbon and use it solely as a chemical filter. In my opinion, the basket is too small to hold enough biological filtration media to provide enough surface area for effective biological filtration.  If biological filtration is the primary goal, there are better choices, but this is a fine performer as a mechanical and chemical filter.

The second possible configuration for the H.O.T. Magnum is to use the pleated micron filter and diatom powder.  This is for exclusively mechanical filtration, or more precisely for very fine water polishing.  This combination is able to remove even extremely small particulate matter from the aquarium water.  The downside is that if your water is very dirty, the filter will fill and clog quickly.  I really like to use a H.O.T. Magnum in this configuration right after I have done a water change and cleaning on a tank.  This way, the filter is able to pick up and remove any waste material that was stirred up but was not captured and siphoned out during the water change.

Marineland Magnum 

Both Magnum Canisters and H.O.T. Magnums can use either a pleated micron filter or loose media basket.

As much as I like the H.O.T. Magnum filters, I have to say that the standard Magnum is my least favorite canister filter.  There are a number of reasons for this.  First, I seem to have more problems getting this filter purged of air in comparison to other units.  I routinely have an air layer trapped in the top off these canisters and it takes a lot of effort to get it out. Granted, the filters will operate just fine with air inside because the manufacturer has located the return pump in the base of the filter (most others locate the pump on top).  But, I still find it annoying to have the trapped air, and it makes the filter run a little noisier.

Second, the media containers are not as versatile as other models.  Like the H.O.T. Magnum, they come standard with two options for filter inserts.  The first is a pleated micron filter insert which is excellent for fine polishing of the water, and the second is a basket that holds activated carbon or other loose media that can be wrapped in a bonded filter sleeve to remove particulate matter.  Unfortunately, these filters don’t have any standard biological media.  They can be upgraded to the "Pro series" which includes a biowheel add on to provide biological filtration, but while I like the biowheels on Marineland’s line of power filters, this add on unit is not a favorite.  I have seen several where the connection from the canister to the biowheel assembly leaked small amounts of water or salt creep.  In my opinion, they also don’t mount onto the tank very well.  The screws that are supposed to hold the biowheel assembly onto the tank seem rather flimsy and are awkward.  All of these downsides could be eliminated if biological filtration was incorporated into the base unit.

Third, the media basket gets crushed easily by the pump’s intake pressure if  the filter isn't cleaned often enough.  When the blue bonded filter sleeve becomes too plugged up with dirt, the pump pulls very hard to try to get water to pass through the filter sleeve.  Because of this suction, the filter basket ends up getting squeezed and deformed.

Lastly, the Magnum comes with four rubber seals that tend to rot over time and require replacement.  Most other brands only use one or two and in my experience last considerably longer than the Magnum’s.  This is yet another maintenance headache and added expense on top of the filter media and basket replacement costs.

Installation Tips

I really like to place all my canister filters inside a bucket when they are running.  This way, the entire filter can be easily carried to a sink for cleaning.  Also, if a gasket is improperly installed after cleaning and causes the filter to leak, the bucket should catch the water.  Lastly, when the filter is disconnected from the hoses for cleaning, a little bit of water sometimes escapes between the valve connections. If the filter is in a bucket it will catch that water before it falls to the floor.

Another thing I like to use on canister filters is a small foam block on the intake to serve as a coarse debris screen.  Since canister filters can be a bit more difficult/tedious to clean, anything that can be done to prolong the period of time between major cleanings helps.  It is far easier to slip the sponge off for a quick rinse in the sink every couple of days than it is to turn off the filter, disconnect all the hoses and plug, haul it over to the sink, take it all apart for servicing....and so on.   Anything that can be done to simplify aquarium maintenance should be utilized.


Eheim filters have a great reputation but were not formally reviewed.

Eheim canister filters are conspicuously absent from my reviews.  The reason for that is quite simple. I have not used enough of these filters at length to feel comfortable discussing or recommending them.  I have only had the opportunity to use three of these in my career and each was a different model.  Although all of them performed flawlessly, my opinion would be based on the extremely limited experience.  Based on Eheim's excellent reputation among aquarists along with my own limited experience, I have recently purchased a new Eheim canister filter to experiment with on a tank that I am setting up for myself.  This article will be updated in the future when I have enough experience with Eheim to give a more reliable review.

Until I experiment with a few more Eheim’s, I am going to fall back on the Hagen Fluval line, Marineland H.O.T. Magnum, or one of the many excellent hang-on power filters I discussed in my July/August Impressions column in Conscientious Aquarist.

WWM on Canister, Cartridge Aquarium Filtration

Related Articles: Freshwater Filtration, Power Filter Impressions,  A review of some popular mechanical filtration systems by Steven Pro,  Setting up a Freshwater Aquarium, Tips for Beginners

Related FAQs: Canister, Cartridge Filters, Canister, Cartridge Filters 2Canister, Cartridge Filters 3, & FAQs on: Rationale/Use, Placement, Media, Plumbing, Maintenance, Troubleshooting/Repair, By Manufacturer: Eheim, Fluval, Other Brands, & Biological Filtration, Establishing CyclingFW Sponge Filters, FW Canister Filters, FW Hang-on Filters, Ultraviolet Sterilizers,



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