When aquariums moved from “fish rooms” to the family room, manufacturers were quick to offer the canister filter as an alternative to the large hang-on-the-back power filters. Unlike power filters, canister filters are nearly silent and hidden out of sight under the aquarium in the cabinet stand. Other advantages include a larger volume for the different types of media, including mechanical, chemical and biological media. Plus, by the nature of the design, all water passing through the canister must flow through the media, so there is no way for the water to by-pass the media. While it takes a little more work to perform maintenance on a canister filter versus the power filter, because of the larger media area, you clean a canister far less often than a power filter. 

Most designs use foam material as their first stage Mechanical filtration. The foam pads will trap fine particles and can be cleaned by squeezing them in a bucket with water from the aquarium. This allows any beneficial bacteria on the foam to survive the cleaning. The foam pad will usually last 9-12 months before it starts to lose its shape and needs replaced. While most canisters filters will include an initial activated carbon filter bag for the Chemical filtration, it is better to use one of the longer term chemical media, like Chemi-Pure, BioChem Zorb or Purigen.  These products can last up to 6 months between replacement. The Bio-Media will usually be either small plastic Bio-Balls or ceramic media, a type of sintered glass that has massive surface area versus volume for colonization by the beneficial bacteria. If need be, the Bio-Media can be tumbled clean in water from the aquarium, and you may need to replace 1/3 to 1/2 of it every year. Given the large range of types and sizes of aquarium set-ups, manufacturers have offered a multitude of sizes and designs of canister filters.  While some are rather specialized, most canister filters can be used with most set-up, it is just some are better at certain stages of filtration.

Below is a brief discussion of the different types and styles of canister filters.


The very first canisters were developed by Eheim back in the 1950’s and were very similar to their current Classic Series. The Eheim philosophy has always been to use the canister primarily as a mechanical/biological filter with a slower flow rate. The Eheim canister filters came with specialized media to perform different functions. At the bottom of the canister, where the water entered, was a layer of Ehfimech ceramic rings. Their purpose was to trap the larger debris and help channel the water flow so that it would flow up the entire column of the canister, not by-pass areas or flow just up one side. The rings are a permanent media and only require tumble cleaning in water from the aquarium to clean.

The next layer was a plastic mesh material that would trap some debris, but was there mostly to separate the rings from the next layer, the biological media, Ehfisubstrat. This is a granular material made from sintered glass. This is glass that has been heated to a high temperature and then quickly cooled, shattering it into smaller pieces that have massive surface area per volume to provide the perfect home for the nitrifying bacteria. This bio-media should also be cleaned by tumbling it in water from the aquarium and replacing one-third of the media every 6-9 months.

At the very top of the Eheim canister is a layer of synthetic fibers (Ehfisynth) to act as a final stage mechanical filter and prevent small particles from clogging the impeller. The initial design simply layered the various media in the canister and had to be dumped out into a bucket for cleaning. Not exactly user friendly, though the Eheim was designed to only require cleaning every 4 to 6 months. The newer Classic design now includes separate media baskets to hold the various types of media.

Eheim was also the first to introduce the newer, user friendly style canisters they call their Professional Series. These revolutionized the entire canister filter market, and nearly all other models are a “clone” of this design. These Eheim canisters have the separate media trays for easy cleaning and stacking of the media, large clamp down clips to attach the motorhead with an integrated O-Ring to the canister body. Also, they have built in shut off valves for the hoses with a quick disconnect feature for when you need to remove the canister from the cabinet for cleaning.

Perhaps one of the favorite features is the addition of a self-priming system to fill the canister with water. The very latest design, the Professional 3 series,  improved on the design by including a coarse prefilter pad at the very top of the canister that allows the user to open the canister, clean just the prefilter, and leave all to other media trays as is. The newest Professional 3e has electronic controls to monitor the flow rate and can be attached to a computer to control the functions of the canister!

Now, if you have been paying attention, one thing you may have noticed is that the “Eheim Way” does not use chemical media. They assert that if you use chemical media, you will have to remove and replace the media every 4-6 weeks, and that is just WAY too much work for them! (They also assume we will have another smaller filter just for the chemical media.) To placate the US market, Eheim does now offer some carbon pads to be used in their canisters, and many hobbyist have been using products like Chemi-Pure or BioChem-Zorb in their Eheim canisters for long term cleaning. One still unique feature they offer on their canisters for freshwater use only is a built in heater and thermostat controller.

The Eheims might still be the leader in design and production but some of the “clones” are starting to catch up.

About The Author Don Roberts

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