My First Angelfish Book

Miscellaneous Pisces

Partner Sites

The Overhead Filter

Gear and Equipment

The Corner Box Filter

Gear and Equipment

The Canister Filter

filed under: Gear and Equipment

I bought my first canister filter, a fluval 304, in 2001. At the time, it was the largest investment I had ever made since I got into the hobby decades ago. More than a decade after that purchase, the filter still works like new. I never had leaking problems nor had to replace any component of the old 304 canister filter, other than filter media of course. And since I usually break things, this filter lasting all these years is a testament to its durability.

Since then I have brought many other equipment yet the original 304 has outlasted some of them. Even now, as I write this article, my first fluval 304 aquarium filter quietly runs in the background filtering 25 gallons of water for a pair of spawning marbled angelfish.

The 304 has been replaced by the 306 (basically the same thing)

Having owned and operated a canister filter for as long as I have, I feel I can now talk about this type of filter with a certain level of depth beyond first impressions (or unboxings) most commonly described in most reviews.

Before we get lost into the topic of conversation, some of you may be asking; what a canister filter is and what is its benefits over other forms of filtration system?

A canister filter is basically a filter that draws water out of the tank, usually through gravity (hence most canister filters need to be situated below the tank), filters the said water in a media-filled sealed container, and draws the water back into the tank through a very strong pump. All this happens in a continues cycle, 24 hours a day.

The main advantage of the canister filter, based on my extensive experience, are benefits not so much to the fish but the keeper of the fish, in this case, the canister filter benefits you more than it benefits the fish. But give me a chance to explain.

Besides its unique setup, higher than average price tag, large media capacity, and a high flow rate pump, the canister filter is not too different to most other types of filters. I would even say that it would be just as good as almost any filter of the same media capacity and the same flow rate pump.

Where the canister filter really shines is in aesthetics and maintenance.


A canister filter can contain a deceptively large amount of filter media. If you have an overhead tank  filter with the same media capacity of, say, the fluval 304, things will get very unsightly. Where as even a very large canister filter double that size can easily be hidden inside the cabinet of some aquarium stands.


The second big advantage of a canister filter comes in maintaining it. Because the canister filter is far away from the fish tank, cleaning it will not disrupt you fish, and their habitat. Most of the time, the wont even know what is happening. This contributes to a stress free artificial ecosystem.

The way I clean my canister filter is by simply disconnecting the unit from the two hoses, opening the unit up to clean or replace filter media,  connecting the hoses back and turning it back on. All this work is done outside the tank, and possibly away from the glass.

Other features and gimmicks

Depending on the make and model, some filters have additional, unique features such as built-in UV sterilizers and a whole other gimmicks. I don't recommend purchasing a canister filter solely for the said gimmicks, but  a "special feature" I really found useful is the adjustable flow rate lever on my 304, which comes useful in keeping slow moving fish like discus or angelfish.

For slow moving fish, a too powerful pump means high water current and is not ideal. Because canister filters have generally strong pumps, without being able to lower the flow rate means you need to install something to disperse the water flow, like rain bar (which is actually a great idea as it lets you have a higher water turn over with out creating a strong water current), or you can get a less powerful canister filter, which also means less filter media.

Other purchasing tips

Because canister filters are expensive pieces of equipment, and more importantly, because will be running 24 hours a day over many years acting as a sort of life-support system for you aquatic ecosystem, you should make sure to do extensive research on the build-quality of the canister filter you are going to purchase.


The Eheim Classic is considered by some as one of the best canister filters ever made.

A leaking canister filter can be an aquarist's worst nightmare and can quickly drain out all the water in a tank due to its siphon design. Therefore it is important to buy high quality filters.

While it is helpful to read reviews on particular items on places such as, I find that most of these reviews are from users who had "just purchased" the product. Many of the positive reviews are only made within a few months of using the product and most of the negative ones are made by people who are in-experienced with, and have misused or misunderstood the product.

Because canister filters will run for years and years, the best advise you could get is actually from people who actually used the same or very similar models for at least 2 to 3 years. They can tell you the strengths and weaknesses of the products, if there are any design flaws to look out for, and most importantly; if these are worth the investment in the long run.

To save you some time, many people who have used canister filters for quite some time will recommend canister filters particularly certain models from Eheim and Fluval. In terms of built quality, the Eheims have a reputation to be the best (such as the classic and pro series), and based on my experience, I could say that you can't go wrong with the standard Fluval line either.

Filter media and spare parts

To me, a good canister filter should be flexible in terms of filter media. Avoid canister filters that uses proprietary filter media such as special cartridges and inserts. Filters that require proprietary media cartridges will limit how you can customize filtration and most likely tie you down to a specific brand of filter media replacements.

Another important thing to keep in mind is that canister filters are complex pieces of equipment. They are made up of several parts and many of them will, in time, wear out and need replacing.

Before you buy a specific brand and model, it is wise to see if parts are available for the product you want to get. The most commonly replaced parts are; impellers components, and gaskets.

Parts for Eheim and Fluval filters are usually readily available from several vendors. Outside Eheim and Fluval line of canister filters, I would suggest doing some research regarding parts availability. Having several vendors supporting, and providing parts for the product you intend to purchase is a good sign that you will be using your filter for a long, long time.