The Ultimate Guide To Canister Filters

Taking good care of our fish tank filters is a necessity and will help us achieve a healthy aquarium with thriving plants and/or fish. Regular filter maintenance and cleaning will ensure your equipment is working effectively providing adequate water flow to your aquarium.

Canister filters may look complicated, but in many ways they’re much easier to clean than internal filters. Additionally canister filters tend to be more effective, customisable and neater than internal filters making them a great option for most fish tanks. 

Perhaps you are completely new to canister filters, or you’re thinking of buying one? Use our simple guide below, filled with maintenance tips to ensure you’re looking after your fish tank effectively…

Read on to discover more canister filter tips…

How to clean an external canister filter

Cleaning your external canister filter shouldn’t be difficult. Use the following steps as a guideline to achieve the best results: 

  1. First gather a basin or bucket that the filter can be emptied into. Towels are also great to have nearby, in case you have any accidents.
  2. Collect a bucket of aquarium water using a gravel cleaner or siphon which will be used to wash the filter media in.
  3. Turn off the canister filter at the plug socket.
  4. Close the canister filter tap valve, and push the button to disconnect the unit from the pipe set.
  5. Carefully unclip the lid of the filter from the canister.
  6. Inside the canister there may be sponges, cartridges, baskets or loose media depending on the brand of filter you have. It may be worth making a note of the order they were removed to make sure they are put back correctly. These will need removing individually and cleaning in the bucket of aquarium water we collected earlier. You can use sponges, cloths and toothbrushes to assist you in this. Remember we are not trying to get them immaculate, but simply remove any thick debris that may have built up. 
  7. Once the media has been cleaned, put them to one side.
  8. Empty the liquid content of the canister into a bucket, basin, sink or drain. You may also wish to wash out the inside to ensure any waste or algae build up has been removed. 
  9. Return the filter media back into the canister in the correct order.
  10. Clip the lid back in place and reconnect the pipe-set.
  11. Top-up the water in the aquarium to a suitable level using dechlorinated water.
  12. Check everything is securely in place, then open the canister filter tap valve.  Allow the water to naturally siphon into the filter from the aquarium which can take several minutes.  
  13. Once you’re sure the canister is full of water, you may now turn the filter back on. 
  14. Clean up any mess that may have occurred and dispose of the soiled water used to clean the media. 


Cleaning the Magnet and Impeller in a Canister Filter

Canister filters contain a magnet and impeller much like an internal filter, allowing them to push water back into the aquarium. This is the only moving part in the canister filter system and is therefore incredibly important and should be properly maintained.

Waste build up can occur around the impeller causing it to slow down or stop altogether. If the water flow in your aquarium seems less powerful or has stopped, a dirty impeller is quite often the culprit! To prevent this from happening, you can remove and clean the impeller occasionally while undertaking your filter clean. We recommend doing this at a frequency of once every 6 months.

Make sure that the filter is turned off when cleaning the impeller. You first need to locate the impeller in the filter - the manufacturer's instructions may help you with this. Carefully remove the impeller by gently pulling it out of its housing. The body of the impeller is best cleaned with a toothbrush while the housing can be flushed out with a jet of water or a cotton bud. Once you’re satisfied the impeller is suitably clean, return it to its housing and reassemble the filter.

The impeller can then be removed from the shaft and cleaned thoroughly before placing it back into the filter. Once the filter has been reassembled and filled correctly it can be turned back on. 


How do you get air out of an external filter?

Air in a canister filter is usually caused when the filter is left full of water before it is turned back on during cleaning. This can create an airlock in the filter, which will usually result in a noisy rattling fish tank filter. Air locks can restrict or even stop the water flow to the aquarium which may damage the filter impeller if left unattended. 

To prevent this from occurring, canister filters should be emptied completely during cleaning. Once reassembled and reattached to the canister pipe-set, the filter valve can be opened, allowing water from the fish tank to siphon into the filter while displacing any air. Leave gravity to do its thing for several minutes! Once you’re confident the canister filter is full it may then be switched back on, and should run quietly and smoothly. 


How often should you clean an external filter?

We would generally recommend cleaning a canister filter every 2 - 4 weeks depending on the stocking levels of your fish tank. If you decide to clean your filter every two weeks and find little waste in the filter, then this can likely be decreased to a clean every three or four weeks. Likewise if you decide to clean your filter every four weeks, and find vast amounts of waste in the filter you may wish to increase the frequency of your filter cleans to three or two weeks. Find a solution that works well for you and your fish!

The best way of checking if you’re cleaning your filter enough is ofcourse by testing your water. Use an aquarium water test kit to ensure the water is free of both ammonia and nitrite. If it is and your water clarity is good, then you’re likely cleaning your filter an adequate amount. 

Can canister filter media be cleaned and reused?

Yes, the media inside the filter can be cleaned out and reused. There will come a time when the media has reached its life expectancy and is no longer functioning at full capability. In the case of sponges they will eventually lose their shape and structure. In the case of biological media they may eventually degrade and dissolve. At this point the filter media will need replacing, however regular maintenance will extend their lifespan significantly. 


Can I clean my fish tank filter with tap water?

Under no circumstances should you use tap water to clean your filter! All filter media should be washed in water taken from the fish tank, to preserve any live bacteria colonies on the media. The chlorine present in tap water will kill any good bacteria existing in your filter, effectively restarting your fish tank cycle, which can result in ammonia and nitrite spikes and upset fish.

If you want to maintain or even add good bacteria to your filter, we recommend regular use of a biological enhancer in your aquarium. This will promote good water quality which will keep your fish in tip-top health. 


How often should I change the filter sponges and ceramics?

If the sponge is starting to lose shape, break down or becomes so clogged with waste that despite your best efforts is no longer coming clean, then it may be time to replace. We recommend  not replacing all the media at once as this will remove the live bacteria colonies in your filter. Instead change one type of media in the filter at a time, whether it be sponges or biological media, leaving several weeks before changing the next.This will give the bacterial colonies existing in the filter a chance to transfer over to the new media.


The same rules apply to any filter floss that may be in the filter. This is the type of media that will need replacing the most often as it quickly becomes completely saturated with waste.

In filters that may only have one sponge. They can be cut in half to prolong the lifespan of the sponges and replace one half at a time. 

Ceramic or other biological media rarely needs replacing. In instances where the ceramics have broken down, we recommend replacing a small amount at a time.

In filters which contain activated carbon, this will likely need replacing entirely in intervals of 3 - 6 months. Normally it is evident when the activated carbon is due to be replaced as the fish tank will lose some water clarity. 

What is the brown gunk in my aquarium filter?

Fish Poop and other organic waste! It is usually a build up of fecal matter, leftover food, dislodged algae, and decaying plant debris that has passed into the filter where it begins to break down. 

If you notice that there is an increased amount of biological waste in the filter you can try cutting back on feeding and/or increasing the frequency of your filter cleans. A large build up of decaying organic matter can contribute to ammonia and nitrite being present in the fish tank which is why cleaning is so important! 


Why is my fish tank filter dirty?

The filter is effectively the toilet of your fish tank. Any waste that has been produced by the fish in the aquarium, is encouraged into the filter system via the water flow. It is then broken down into various compounds as it passes through the media. The clean water is then returned to the aquarium by the impeller, through the return valve. This cycle is happening continuously. 

When the filter is dirty it may negatively affect the health and performance of your aquarium. You may notice a decrease in water clarity and/or an unpleasant odor from your fish tank. These are tell tale signs that there is a build up of waste and the filter clean is now overdue. 

When you open up your filter you will be able to see all the waste that has been collected. Some of the waste will be thick which is generally caught on the most coarse sponges, while the finer matter will be present on the medium/fine sponges and filter floss. 

When undertaking a filter clean you will remove the majority of the waste from the filter, so that the process can start all over again. 

Find the best Canister Filters for your aquarium, at Complete koi and Aquatics

Here at Complete Koi and Aquatics we are proud stockists of some fantastic, tried and tested canister filters. 

We have a great selection of manufacturers and sizes, to cater for all sizes of fish tank. If you’re looking for a powerful filter, and crystal clear water make sure to check out our website today!

If you’re looking for any advice on choosing the right canister filter for your set-up, don’t hesitate to reach out to us directly. Click here to get in touch today


Shop the best aquarium products & accessories for your freshwater fish at Complete Koi today

For more information and advice on aquatics, check out the rest of our blogs…


Buying Guide: Aquarium Filters | Keeping Tropical Fish: How to care for platyfish |The Best Freshwater Fish For Your Aquarium

The cookie settings on this website are set to 'allow all cookies' to give you the very best experience. Please click Accept Cookies to continue to use the site.
You have successfully subscribed!