Why Canister Filter Flow is Reduced Significantly?

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Canister filters are some of the most reliable filtration systems you can get. They take up no tank space, are easier to clean than other filters, and don’t require a lot of maintenance.

They also offer mechanical, biological, and chemical filtration, keeping the water clean and better-oxygenated for your aquarium life.

But what happens when the filter starts to lose its power? This can happen at times, especially when skipping maintenance day one too many times.

5 Reasons Canister Filter Flow is Greatly Reduced

Each aquatic setup requires a specific water flow based on the layout and the type of plants and fish you’re housing. The flow ensures healthy water circulation, allowing fish to breathe better and moving water residues into the filter’s intake.

If there is no flow or the flow is greatly diminished, the filter’s entire presence is rendered obsolete.

So, you need to fix the problem asap. Everything begins with identifying the causes, so let’s look at the 5 most common filter-related issues:

1. Clogged Water Tubing

The filter’s tubing system transports the water in and out of the filter. The problem is that the filter’s tubing makes for a static system, unlike the impeller and motor unit.

So, it’s far easier for the tubing to collect sediments that will eventually restrict and even stop the water flow.

Interestingly enough, the color of the tubbing can minimize or maximize the problem, depending on the circumstance. For instance, transparent tubes take in extra light, which, when combined with the present moisture and residues, promotes algae growth.

So, algae can actually grow inside the tubing to clog the mechanism with time.

You can minimize or even circumvent the problem by having darker and opaque tubes that keep the light out.

However, this doesn’t fix the overall issue, which is the accumulation of gunk and dirt inside the tubbing with time.

This can happen faster if the tank is overpopulated with fish and plants and based on factors like:

  • How many food leftovers accumulate over time
  • How much poop your fish produce since some fish are messier and more poop-proficient than others (goldfish, I’m looking at you!)
  • Whether you have bottom diggers that disturb the substrate often, blasting dirt and substrate particles in the water column
  • How much waste and dead matter your plants produce, etc.

Generally speaking, the canister filter requires generalized cleaning once every 30-60 days, depending on the context. The issue is that the tubbing can lose some of its power due to the aggravating factors we’ve just mentioned.

In that case, arming your filter’s intake with a filtration sponge can mitigate the problem considerably.

Just ensure you inspect the sponge regularly because it might require frequent cleaning or replacement.

2. Dirty Mechanical Media

The purpose of the filter’s mechanical media is to collect larger floating particles like dead plant matter, food residues, substrate particles, fish waste, algae, etc.

These will eventually accumulate on the media in bulk, restricting the airflow with time and dropping the filter’s effectiveness.

At this point, you need to clean the filter media to remove the dirt deposits.

When doing so, make sure you:

  • Only clean the filter with tank water because tap water contains chlorine which can kill the beneficial bacteria inhabiting the media
  • Don’t overscrub the media; only eliminate visible deposits that restrict the component’s effectiveness
  • Don’t use any cleaning chemicals like bleach, vinegar, or soap which can sterilize the media and destroy the bacterial colonies
  • Don’t clean the media too often; only when it’s clear that it requires maintenance

In essence, the mechanical media requires regular cleaning to keep the filter running at full capacity. How frequently you should clean the filter media depends on a lot of factors that we’ve already discussed.

These include the tank’s layout, how many food residues accumulate in the water and how fast, how much fish waste fish produce, etc.

3. Broken or Clogged Impeller

The impeller is a critical component in any filtration system. It’s actually what creates the water flow by spinning and creating centrifugal force inside the mechanism.

Needless to say, if the impeller breaks, the whole system fails.

There are several issues to keep in mind in this sense. The impeller can:

  • Get clogged due to accumulating dirt and debris with time (algae deposits are also possible, although unlikely due to the water flow in the area)
  • Get damaged due to sucking a rock or any hard particle that could impair the component
  • Get overheated due to lack of lubrication and maintenance

Fortunately, you can typically tell that the impeller is the cause of your flow problems. The impeller will generally generate a specific rattling sound when facing clogging or any other type of problem.

Pay attention to your filter’s audible inputs and check the impeller if anything sounds unusual.

Also, cleaning the component regularly is great at preventing some of these issues.

4. Flow Rate Regulator

Automatic flow rate regulators are great additions to any filtration system. Especially when using a larger filtration system compared to the aquarium’s requirements.

Many people get larger and more powerful filters with flow rate regulators in case they decide to increase their tank’s size later on.

So, they will use the regulators to drop the flow rate enough to match the system’s requirements and increase it after upgrading the tank.

This means that, when the flow regulator breaks or gets clogged, the filter’s flow rate will drop with it.

The solution? Unmount and clean the regulator and test it out again. The problem is more likely one of mechanical nature.

5. Motor Problems

The filter’s motor is its heart, putting everything else in motion. For one, the motor controls the impeller, which means that if the motor fails, the impeller fails with it.

Fortunately, whatever affects the impeller affects the motor as well. If the impeller accumulates gunk and starts operating at a lower rate, the motor is forced to push through the additional resistance.

This can cause the filter’s motor to overheat and lose much of its power output. Check the motor if you notice an unusual sound in the impeller or motor area or if the canister’s casing is hot to the touch.

It may be running overtime, causing it to overheat.

The problem is easily fixable in most cases, as cleaning the impeller will usually restore the motor’s normal functioning.

How Does the Flow Rate Affect Filtration?

The filter’s intake sucks in environmental water, carries it through the filtration system, and pumps it out via the output. Reducing the filter’s flow rate is essentially the same as reducing the amount of water it can process.

This will decrease the filter’s overall power and efficiency, reduce the waste it can clean, and drop water oxygen levels.

So, you need to make sure that your filter is in peak operating condition. Regular cleaning and inspection are necessary to keep your canister filter in optimal shape in the long run.


Canister filters are easy to clean and maintain over time. Perhaps this is why so many people skip the maintenance day; it’s easy to do that when your filter seems to work just fine.

But remember, your filtration system may require cleaning even if it doesn’t look like it. Adapt the maintenance schedule to your unique situation and stick to it.

This will both prolong your filter’s lifespan and keep the aquatic system healthier and cleaner overall.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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