What Is The Best Filtration Media To Use In A Canister Filter?

Canister filters have been around for decades. They’re usually shaped like a canister (strange that) but can also be square. The media sits in the canister under the ’lid‘, and it is in or on the lid that an electric motor is placed. Water to the filter arrives via a flexible tube, and is returned by the same method. Canister filters were used, and still are, by freshwater aquarists, and have been adopted up to a point by the marine hobby.

Canister filters are very reliable though some makes, as in most things, are better than others. There are a couple of points that need mentioning. The first concerns flow rates. It is the habit of many manufacturers to quote flow rates for an empty filter. Without the media in position the flow rate will be higher, so in the real world expect the flow rate to be perhaps up to a quarter or so less. Flow rates are additionally slowed by the lift – if a filter is placed on a level with the aquarium there is little or no lift, if it is below the aquarium the electric pump has to lift water from the filter to the highest point before entry to the aquarium. It is important to know this distance and check the filter performance from manufacturer’s data.

Ok, back to the media. The question could be taken three ways. What is the best media to use in relation to a marine aquarium, the best for bio-filtration, and the best for mechanical filtration.

As far as marine aquariums are concerned, the bio-filter media of choice is good quality live rock, in my opinion. Therefore the canister filter, using this as a “rule“, would be redundant as a bio-filter. There aren’t any rules, however, and though the canister filter is not the best bio-filtration method to use overall it is not redundant in this respect. Nevertheless, if live rock is to be employed, the canister filter is demoted to mechanical filtration.

If the canister is to be used for bio-filtration, then some care on the media set-up is needed. Bio-filtration is the ‘life support’ for the livestock and obviously is very important. Though it may be against some manufacturer’s suggestions, I have found that having all the mechanical filtration in front of the bio media is advantageous. I found a fine filter, sandwiched between two medium grade sponge filters, does an excellent job on protecting the bio media from debris. It is very important that the mechanical filtration is cleaned at regular intervals (the period dependant on the cleanliness of the water, perhaps every two to four weeks). In addition to helping to keeping the bio media clean, it maintains water flow. The bio media available is varied, however sintered glass, which is in the form of small tubes, seems very good. As there are lots of channels within the glass, it can act somewhat as does live rock for a while. In other words, nitrate can be reduced by bacteria. This benefit is usually not long lived however, as fine debris does inevitably find its way onto the media causing some clogging and the anti-nitrate advantage is lost sooner or later. (This media should not be used intentionally for any anti-nitrate properties.) The media still remains very good for ammonia/nitrite filtration. The media, if cleaning is required, should be gently cleaned in warm aquarium water, never in tap water. The latter will wipe out the bacteria. A final point to note when bio-filtration with a canister filter is employed, is that the unit will usually produce nitrate (perhaps not straight away as indicated). When nitrite has been converted to nitrate, the nitrogen cycle stops. If there isn’t a low oxygen environment for bacteria to inhabit, then nitrate will remain. A check needs to be kept on the level.

If the filter is to be used for mechanical purposes, then the same mechanical filter media as above can be employed. This media can begin with medium grade sponges, perhaps two layers, and end with fine grade filters. Many manufacturers provide ready made filter materials such as sponges so the fit in the filter is good. Manufacturers usually give suggestions for mechanical filtering. In addition, activated carbon can be used in the filter. It is usually placed after some mechanical media. Activated carbon is not always a necessity, and should not be used continuously if there is a need but periodically. The media removes trace elements from the water. When exhausted (manufacturers will suggest life expectancy) the media should be discarded, if more is required it should be new. Similarly, anti-phosphate media can be used. This can be used continuously if necessary, changing the media at the manufacturers recommended periods. Some anti-phosphate media has a tendency to clog and/or channel, making it far less useful. The types that do this are usually the ones with very fine media.

So the canister filter is useful to the marine aquarist. It is not ‘number one’ for bio-filtration, but can still be used as such, with success provided the aquarist maintains it properly. The filter is also useful for assisting in the removal of debris from the seawater etc. Some aquarists, having a canister filter available and not requiring filtration from it, have experimented with other media, such as small pieces of live rock debris and very coarse sand. I don’t know the results of these experiments, but I do know that in my canister filters using standard media, when doing maintenance I always have to remove very small shrimps and snails and return them to the aquarium.

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  1. I dont use a mechanical filter other than a HOB Skimmer. I thought about getting a canister at one point but I have been told many mixed stories about them. Mostly that they become bad nitrate factory’s.

    ChehalisCoral’s last blog post.. Rabbit Fish To The Rescue Of The Reef

  2. Canister filters are nitrate factories. Then, so is live rock and any other filter that deals with the nitrogen cycle. The difference is that the nitrogen cycle stops at nitrate with a canister filter, and other means (eg. water changes, denitrators) are used to remove the nitrate. Live rock of good quality and adequate quantity achieves the full nitrogen cycle, converting nitrate to gas which can then escape from the aquarium.
    If the amount of ammonia initially present is the same, then each filter of whatever type will produce the same amount of nitrite followed by the same amount of nitrate.

  3. Quick addition to the above – in respect of nitrate I’m talking of a canister used as a bio-filter.
    Canisters used as mechanical filters don’t develop much bio activity because of regular media cleaning under the tap and the fact the main bio filtration (competition) is elsewhere, thus nitrate is not a problem.

  4. Will lift really matter? Isn’t a canister-filter working like a closed loop?

  5. Well spotted Espen, canisters are working like a closed loop. The main drop in flow rate is when filtration media is added. Thanks.

  6. john you dont rinse canister filter media under the tap, you kill the bacteria, you rinse it thro water that has been takin from the tank when doing a water change. do you actually know what your talking about on here, or you just winging it,

  7. Hello Thomas. Try reading the text! Paragraph 5 “The media, if cleaning is required, should be gently cleaned in warm aquarium water, never in tap water. The latter will wipe out the bacteria.” It seems quite clear. The only time tap water can be used to clean canister filter media is when the media is purely for mechanical filtration.

  8. So to the beginners Im kinda confused I have a 90 reef/fish tank I have 100 lbs of live rock a bubble magus skimmer and a mechanical sock I bought a rena xp4 canister filter to mainly run carbon through it and I bought some biomax bio rings for Beneficial bacteria but now I think its a little over kill. my tank has been up and running for a year now any help would be great thanks

  9. Hello Dan. Basically a marine aquarium is a simple set-up but it can get confusing with all the different equipment and methods.
    At its foundation a marine reef system needs three things: high quality seawater (which means an efficient biological filtration system to get rid of the toxins ammonia and nitrite and maybe nitrate, plus an efficient skimmer), acceptable lighting for corals, and agreeable reef layout to afford security for the inhabitants. Your skimmer is necessary as is your live rock. It is advisable to have mechanical filtration as well often provided by canister(s).
    You have a reef system, it has been active for a year and there isn’t any problem mentioned, therefore it is assumed your seawater quality, lighting and layout are fine. As it is running well with the inhabitants healthy then any changes made should be with caution.
    You have the best biological filtration available – live rock. When of decent quality and sufficient quantity it will deal with ammonia, nitrite and within reason nitrate. The guideline suggests 1.5 lbs per gallon as ‘enough’. However there is a problem with this as there are varying types of live rock which weigh differently so dealer advice is usually sort. However, as said your system has no problem mentioned.
    A canister filter of proper size for mechanical filtration of the system is often used for more than one purpose. The main purpose is for fine and coarser mechanical filtration of water born debris. Secondly, sometimes a layer of carbon is placed in the filter often on an alternating ‘with and without’ basis. The filter should be cleaned regularly and on this occasion a layer of carbon is put in. At the next clean the carbon is taken out (say one or two weeks later) and left out. Then at the next cleaning point fresh carbon is put in and so on. Old used carbon is thrown away. The downside of carbon is that it removes some trace elements as well as the helpful removal of some organics. Many aquarists (including me) don’t use it. Regular partial seawater changes plus an efficient skimmer should keep the seawater ‘sweet’. Try this very simple check usually called a ‘gilvin’ test. Gilvin, or yellowness of the seawater, is the end product of bacterial breakdown of organic matter. Put a piece of white paper at one end of the aquarium on the glass then look at it through the seawater from the other end. Is there any sign of yellowness? If not, don’t bother with the carbon.
    Putting bio rings in the filter will not do any harm and helpful bacteria should develop. However, it is likely that there isn’t any need, the live rock should be sufficient (your bio-load caused mainly by fish is unknown and presumably overfeeding is avoided). If you decide to remove the bio rings (which will provide more space for mechanical filter material) the system shouldn’t suffer. Nevertheless use caution as any bacteria in the canister could be taking a little of the work from the live rock bacteria. Remove some bio rings weekly, say a quarter of the total and keep a close watch on the livestock. Also test. Once all the bio rings have been removed and the livestock and tests are fine then all should be well.
    Another downside of bio filtration using a canister is that after the removal of ammonia and nitrite the cycle stops. Nitrate is produced but not removed as it could be by live rock.
    I’ve not come across a ‘mechanical sock’ but if it does a good job at mechanical filtration and is easy to maintain then its use or not is a personal decision.
    May I repeat – use caution and carry out any changes to the biological filtration slowly. It is very difficult to judge from afar. The simple check is that if the reef inhabitants are healthy and happy then all should be well.

  10. John thank you so much for taking time to respond to me very informative I don’t like asking a lot of questions I rather do a lot of research but so many people say so many different thing but I’m going to stay away from the canister my tank has had no problems not one lose knock on wood my levels have been great my tank is well maintained once again thanks for helping a novice

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