Canister Filters – How They Work – In a Nutshell

Canister Filters– How They Work


Quite often, people ask, “How does a canister filter work?”  Understanding how a canister filter works may lead to a better maintenance schedule and a better understanding of what is exactly going on in that “cylinder-like plastic thing with a motor” that sits beneath your aquarium stand


Canister Filters:

Canister filters are generally mounted underneath a stand and tucked away out of sight.  Inlet and outlet fittings constructed of either plastic or metal and sometimes glass, hang on the tank and are connected via tubes (usually vinyl) which allow the water to flow in and out of the filter.  The inlet and outlet tubes are often times adjustable and may offer multiple options for the water to enter back into the tank; e.g. spray bar, jet return, lily pipe, etc.

The filters can be powered by either an internal motor or by an in-tank pump that forces water into the canister.  All of Aquatop’s canister filters have internally mounted motors and rely on gravity to start the system.  Once the filter is filled with water, the internal pump then powers the system by forcing water out of the filter, up the return tube and back into the tank through your filter’s outlet.  The location of the internal pump varies by manufacturer but conceptually they work the same.  Canisters that are powered by in-tank pumps are not reliant on gravity to start the system as water is being forced into the filter and not gravity fed. 

Internal Motor or In-tank Pump?

Well, why would I want one over the other? Most manufacturers have incorporated the motor internally.  An internal motor means that there is no pump taking up space in the aquarium and you don’t need to have another power cord coming out of the tank. Internal motors are easily cleaned when servicing the entire filter and you don’t need to reach into the tank and deal with a dirty pump. Utilizing an in-tank pump can give the user room for adjustment in flow as it is quite easy to swap pumps to add or decrease flow.  Be mindful that adding flow to a canister will increase pressure and may compromise the seal.  Always consult your owner’s manual for maximum recommended flow rates.  Canisters with internal pumps are engineered to operate at the specific pump’s flow rate and internal pressure should not be an issue. 

Water Flow

How does the water pass through all of the filtration media?  Some units filter from top-to-bottom and others vice versa.  Aquatop canisters flow from bottom-to-top.  The water enters the canister from the suction that the pump creates and travels down a specially constructed cylinder that minimizes dirty water bypass until it reaches the bottom.  The water then exits the cylinder and travels up through the multiple media trays, cleaning your water, and then exits out of the return tube and back into your tank.  A canister with an in-tank pump works nearly identical.  Some manufacturers utilize chambers instead of media trays; however, the end result is that water passes through a dedicated area of your selected media.

Servicing your Canister Filter

Servicing a canister filter is generally very straight forward.  You disconnect the tubes from the filter head via a disconnect valve that generally stops the flow of water.  Next, you transport the filter to your designated service area and begin taking it apart per the owner’s manual or whatever service instructions that you have.  When servicing the filter, always be sure to remove any grime or debris from the impeller.  Electromagnetically powered motors, very commonly found in the aquarium trade, rely on magnetism.  The impeller is the magnet and the motor rotates creating a magnetic field that effectively spins the impeller.  When the impeller is coated with gunk, the magnetic field strength is compromised causing a reduction in the performance of your filter.  If the impeller gets too dirty, it may actually stop spinning and since the motor is still spinning, the chance of overheating your motor is very likely.  Magnetic motors in liquid applications rely heavily on the liquid they are moving as a means of cooling, just like your car.  If there is no liquid moving then you are heating and we certainly don’t want that from our filter motor!  Want to know more on magnetic pumps?  The internet is your best friend. J

Flow Rate:

Often times people purchase filters based off of a certain flow rate.  Companies, including Aquatop, include these numbers on their product box to give customers an idea of what capacity the filter can effectively clean based off of a certain turnover rate.  A common turnover rate in a fresh water aquarium is 3-5 times per hour and that is what most companies will assume when specifying the capacity capabilities of their filter.  Your turn cycle should be tailored to your livestock as every fish has different requirements.  A common misconception is that the flow rate listed on the box is the effective flow rate coming out of the canister and into your tank.  While this is partially true, it is recommended to measure the head height of your system, or the height from the top of the canister to the spot on the tank that the return fittings hang on.  This head height should then be applied to a table or graph that manufacturers publish that let consumers know how fast the filter will flow at “Y” height.  Having trouble understanding this?  Imagine you have a garden hose without any type of nozzle.  If you aim the hose straight up, the water will travel a few feet and then fall back on itself.  If you want to make the stream go higher, you either increase the power of the pump or you increase the velocity of the water.  This same principal applies.  The further the water has to travel, the more it will slow down and if the path is too high the pump may not be able to overcome the power of gravity.  If you are still having trouble grasping this concept, give us a call and let us help you figure out what the best option for your setup is.  Sometimes too much information is daunting, but knowledge is contagious! 


Additional Questions? Give us a call at 562-697-9860 or Toll Free at 888-915-2782



Benjamin Webster

Enthusiast, Technical Support, Aquatop Sales Account Manager and Email Marketing Coordinator

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