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

Benefits and Functionality of Carbon in your Aquarium Filter



Possibly the most versatile media one can install into their filtration system.  Whether it is a hang-on-back or canister filter, carbon should almost always find a home in your aquarium system.  Carbon is the building block of life and is manufactured through the use of either coal or wood and is used in various industries from fish keeping, to automotive, to cycling, to board sports and a plethora of others.  Many people overlook or do not care to know the abilities of carbon to help their water quality. Part of it may be lack of understanding, but maybe we can help with that.

What does it do? Why is it so important?

Carbon, when used in an aquarium application, is a form of chemical filtration that is capable of doing a multitude of things.  It helps remove odors, discoloration, medications, organics and inorganics from the water by allowing those particles to bond or become trapped by the pores in the carbon.  It also helps water clarity by polishing the water, more so then a fine filter pad. The finest of filter pads still have larger pores then carbon, rendering carbon a powerful tool in removing particles at the microscopic level. BUT, be sure to use a filter pad to prevent the carbon from prematurely gunking up.

Trapping the particles in the pores is called absorption; just like a sponge, it provides a porous surface area for particles to get ‘stuck’ in.  One may ask, “If it’s like a sponge, can’t I just rinse it?”  There is another process called adsorption; notice a “d” instead of the “b.” This process actually chemically bonds particulates, therefore trapping them in the chemical makeup of your carbon.  Particulates that are adsorbed cannot be removed by any conventional standards.  Think of it like baking a cake; all of the ingredients are separately added and the outcome is drastically different then a bowl of eggs, milk and other cake batter ingredients.  Now think if you wanted to back track while making a cake; you would have to go to a science lab and chemically extract each ingredient and even then, that may not be possible as the protein in the milk may have bonded with the egg whites, and so on.  So once your water smells or is becoming discolored; it’s time for new carbon.  No matter how much you rinse your carbon, it is effectively useless for chemical filtration once all of the pores are clogged.

Investing in a high quality activated carbon will help ensure that your filtration system is performing at its best by providing an ample amount of pores for particles to stick or bond to.  Replacing your carbon monthly or when your tank begins to yellow or smell, will ensure that your water is healthy.  Having trouble telling what color your water is?  Try pouring a cup full of water into a clean toilet.  Does the toilet water change color?  If so, time for new carbon!

-Ben Webster

Aquatop Aquatic Supplies

How to Setup an Undergravel Filter on Aquatop’s ST-Series of Tanks

Setting up an undergravel filter is often times quite simple.  There are usually a minimal amount of pieces and the setup is generally very straight forward.  Aquatop’s ST-Series of Bowfront tanks are supplied with an undergravel filter and occasionally customers ask, “How do I set this up?”

There are approximately four parts included with the Aquatop undergravel filter. 

  1. Undergravel Plate
  2. Powerhead/pump
  3. Uplift tube
  4. Return spout

It should be duly noted that the substrate in your tank should by no means be able to pass through the undergravel plate.  Substrates small enough to pass through the plate will likely impede the impeller on the powerhead/pump and may cause the pump to malfunction.


The above picture shows how the filter looks when it is setup. The location of the plate is subjective to the person setting up the tank and does not have a proprietary or mandatory location.  You may consider placing the the plate in an area where fish are more likely to “do their business.”

Below you will find pictures of one of our office tanks.  It is an ST-320,, done up with a nice earth colored substrate




As you can see from the above pictures, the overall setup is rather inconspicuous and even better, there is nothing hanging on the tank! You may also notice that there are no fish in this tank.  It is presently going through the nitrogen cycle and has been setup for about 4 days.

Want to know more?

Here is a link to an informative Youtube video that I came across while putting this article together.  The dynamics of undergravel filters are explained quite well and should offer a better understanding as to exactly how this sponge-less design is so effective.


Thank you for reading!


-Ben Webster

Aquatop Aquatic Supplies,, Hobbyist, Aquarist

Protect Your Fish!

Promote a healthy aquarium system by utilizing a UV sterilizer…

As fish keeping grows in popularity, so does the demand for effective ways to help protect your fish from parasites, fungus and bacteria.  All of the aforementioned can lead to livestock losses and sometimes the departure from the hobby. A UV sterilizer, although not a stop-all to bacterial infections, fungal outbreaks and parasites, is a very effective way to keep your aquarium system at its absolute healthiest. 

Installing a stand-alone UV sterilizer, canister filter with UV integration or hang-on-back filter with UV will decrease the risk of harmful outbreaks in your tank by “zapping” organisms that pass buy the powerful UV-C bulb, leaving your fish happier and you less stressed!

Apart from helping control harmful organisms in your tank, it has been proven time and time again that UV sterilizers work fantastic for algae control.  Many customers buy UV systems just for water clarity.  Whatever your reason be for needing UV in your tank, you will have no regrets.  Just imagine your fish smiling back at you.

-Ben, employee and Aquarist


The above and below are pictures that customers sent after about a week of UV Sterilizer use.


Aquatop’s New AF-400 Professionally Reviewed

The new Aquatop AF – 400 Canister Filter is an excellent and unique addition to the filtration options available to hobbyists. I have mine on a 120 gallon tank that is home to 9 almost fully grown F1 “Peruvian Altum” angelfish, plus some large plecos, 6 rams and a bunch of catfish. The AF – 400 is rated at 396 gph, and has simple to position intake and return tubes. The compartments in the filter allow for easy placement and cleaning of filtering and biological materials. Two innovative components of the AF – 400 that make it an excellent filter are 1) the self-priming switch, which fills the filter with water without any siphoning required, and 2) the integrated UV bulb that can be switched on/off as desired. I would strongly recommend the AF – 400 for any hobbyist looking for a top-of-the-line canister filter.

David A. Lass —

Has been keeping aquariums since he was a kid in the late 60’s. He started a chain of four retail pet stores and a wholesale import/distribution company. He currently imports fish, and wholesales to stores in New England. In addition to his fish room for the wholesale business, David keeps a number of large display tanks and koi ponds.


CF Canister Filter Hosing Length Recommendations

Aquatop’s CF-300/400/500 canister filters are supplied with 6-feet of hose per side.  It is not recommended to exceed the 6 foot hose length when setting up your system.  For easier and faster start-ups, it is highly advisable to cut the hoses so that they are as straight as possible entering into the canister. 


Thank you

BW – TA Team

Welcome to truAqua .com!

The One-Stop Shop for All Your Aquatic Needs! Whether you are in the market for a canister filter, wave maker, LED aquarium light, or even a new fish tank, TruAqua has all your aquatic products in one place at the lowest possible price. We close the gap between quality aquatic hardware and affordability with factory-direct pricing on heaters, filters, lighting, all-in-one aquarium systems, and so much more. Factory Direct Pricing Means Huge Savings. The aquarium products you see here are manufactured by some of the best overseas factories in the world. We scout the best possible aquatics products at the lowest possible prices and then pass the savings onto you. We Love This Hobby Too! TruAQUA is staffed by people who share a genuine love for aquatic creatures. We will always provide you with great customer service because we love what we do. Whether you own a small fresh water setup or a 300-gallon saltwater dream, we guarantee that you’ll find the right product at the right price. Happy hunting!