Fish Tank Filter Not Working? Here’s Why…

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Is your fish tank filter not working?

Aquarium filters are essential in this hobby, so when they stop working, you can expect some problems! But what should you do if your filter malfunctions? Well, don’t rush off to buy a new one too soon because there’s a good chance you can fix it yourself!

In this guide, I’m going to help you get your aquarium filter up and running again. We’ll start off with some pretty obvious stuff and progress to more technical issues, so read through until the end and you should have the solution you need.

Key Takeaways

  • Aquarium filters can stop working for many different reasons, but it’s often possible to fix the problem at home.
  • Start with the simplest solutions before taking drastic actions. Sometimes all you need to do is check your filter’s electrical plug.
  • A lack of aquarium maintenance can cause various filter problems, so invest a little time every week or two to inspect and maintain your equipment.
  • ELECTRICITY IS DANGEROUS. Unplug your filter before inspecting it and please leave electrical work to competent individuals.

Troubleshooting – First Steps and Clues

Are you sure it’s not working?

This may seem like a silly question, but some filters are almost completely silent so you really need to look or feel to know if they’re running. Look for water flow near the filter’s outflow to know if water is moving through the pump.

If you’re sure your filter is not running, it’s time to figure out why.

When did it stop working?

Doing a little detective work can help you figure out some potential causes of your fish tank filter not working.

Let’s take a look at a few scenarios:

  • After a power outage: Some filters need to be primed each time you start them. So, if your power went out, you might be able to re-prime your filter and get it up and running again.
  • After a power surge: Lightning strikes, tree falls, and power outages can all cause surges that could damage electrical equipment1.
  • Gradual loss of performance: If your filter has been weak or noisy for some time, it could be a sign of a clogged impeller or filter media. These problems tend to build up over time.

Fish Tank Filter Not Working – 5 Possible Causes

Finding the problem with your aquarium filtration system is much easier when you know where to look. Continue reading to discover five possible causes and what you can do to solve them.

1. Power Problems

Aquarium filters need electricity to run, so that’s the first place to look when your fish tank filter stops working. Before we go any further, I just want to remind you of something obvious: ELECTRICITY IS DANGEROUS. Please leave electrical work to trained professionals.

With that out of the way, let’s look at some safe tests that you can do.

  • Check the power source

If your filter isn’t running at all, don’t be too quick to assume that the filter is the problem! The issue could also lie with your power supply, power strip, or any of the connections between your electrical panel and the filter itself.

Start by making sure the filter is plugged in at a power outlet. Some outlets have a dedicated on/off switch, so make sure that’s in the ‘on’ position.

If it’s definitely plugged in but still not running, your next step is to test the outlet. You can do this by unplugging the filter and plugging in a different electrical appliance like a lamp. If that doesn’t work either, your filter is probably not the problem.

  • Check your power strip

Sometimes there’s nothing wrong with the power source or the filter. Your powerstrip might be faulty or need to be reset. Some power strips include a reset button that will need to be pressed after a power surge or overload.

  • Inspect the cable

Electrical cables are pretty prone to damage, so it’s a good idea to visually inspect them for signs of wear or breaks. If you’re handy, you may be able to repair a worn cable yourself, but I recommend getting help from a pro if you’re not sure.

  • Are you using a timer?

It’s best to set your aquarium lights on a timer to keep a regular day/night schedule. However, your fish tank filter should be set to run constantly.

It’s annoyingly easy to get your plugs mixed up during the aquarium cleaning process, and sometimes the solution is as simple as switching plugs! If this happens to you, consider putting a zip tie or some colored tape on your filter cable to help you identify it easily.

2. Clogged Filter

Beneficial Bacteria from Existing Filter

Your filter is designed to collect debris from the water, but sometimes, these waste particles build up to such an extent that they create blockages that prevent your filter from working properly.

  • Rinse regularly

Many fish tank filters use a synthetic sponge material as a filtration media. These sponges do not need to be replaced until they begin to fall apart, although they do require regular maintenance to avoid blockages.

The dirt that collects in your aquarium filter media will reduce water flow and mechanical filtration, but you can avoid this by simply rinsing the sponge outside of your aquarium in some tank water. Avoid using chemicals or hot water when cleaning your sponge media as this can kill the good bacteria that are essential for proper filtration.

Check out my detailed guide to the aquarium cycle to learn more about beneficial bacteria and the nitrogen cycle.

  • When to replace

Some filters are designed to use cartridges that must be replaced regularly. This type of media should be replaced at the intervals recommended by the manufacturer to avoid a reduced water flow rate. Filter floss is another filter media that clogs easily and will need to be replaced regularly.

3. Air Locks

Sometimes, air gets into the filter and causes an air lock which reduces your flow rate or even prevents your filter from moving water. This often happens when the filter intake is not positioned below the water’s surface, although it also occurs if you run an airstone near the intake. You may need to prime your filter to get it restarted, although the procedure will differ depending on the type of filter you have.

  • Hang on back filters

Many hang-on-back (HOB) filters need to be primed before they can operate or they may be very noisy and fail to operate correctly. However, some models have self-priming technology.

To prime a HOB, simply fill the impeller chamber with water from the aquarium until it begins to flow through the outflow and back into the tank. Then, you can adjust the flow rate to suit your needs.

  • Canister filters

Many canister filters have self-priming technology, but some must be manually primed using the built-in pump. You may also need to rock your canister filter back and forth or side to side to dislodge any air trapped in the impeller housing. These filters should be placed below your aquarium for best results.

4. Disrupted Water Flow

Each aquarium filter type works differently, but they are all designed to suck water from the aquarium and pass it through some sort of filter media. The obvious exceptions are sponge or under gravel filters that work with an air pump.

Your filtration system will not work properly if water can’t flow through the media as it should, so it’s important to inspect your filter and ensure that everything is clean and put together properly.

  • Water intake obstructions

The water intake is a common source of problems since this is the first place where blockages can occur. Inspect the intake grid or tubes for obstructions like plant leaves or hiding snails.

Sometimes, the intake tube of your filter may become dislodged, which disrupts the flow of water through the system. Make sure this component is seated properly as it can make a huge difference.

  • Flow valves and flow rate adjustment

Many modern aquarium filters come with an adjustable flow rate, so this is a good place to start if your filter just seems a little weak. Check out your user manual or look for a dial or lever to increase the flow rate.

Canister filters have valves on both the intake and output valves. Water will not be able to flow through the canister if either of these valves are shut, so make sure the tabs of each valve are in the open position, or at least open enough for water to pass through.

  • Water level in the tank

Over time, water will evaporate from your aquarium, leading to a slow decrease in water level. If the level gets below your filter’s intake, the unit will begin to suck air, and it may overheat or malfunction. Keep your aquarium full with regular top-ups and water changes.

5. Filter Motor Problems

  • Clogged impeller

Internal power filters, canister filters, and hang-on-back filters all have a part known as an impeller, and this is a very common cause of filter issues.

The filter impeller is the part of the pump that spins, creating a water current that sucks water through the filtration media and back into the tank. Sometimes, this crucial part becomes dislodged from its correct position or it may get clogged with gravel or wrapped up in fibers or hairs that prevent it from spinning.

  • Impeller maintenance

You can usually access the impeller pretty easily without any special tools, but make sure the filter is unplugged before opening it up. Gently remove the impeller with your fingers or a pair of tweezers and clean it off, paying attention to the blades and the steel impeller shaft. You should also look for obstructions in the impeller housing and clean it out if necessary.

  • Impeller replacement

You can often get your aquarium filter back up and running by simply cleaning out the impeller and housing, but eventually, you might need to replace some parts. Impellers don’t last forever, so order a replacement when yours becomes grooved, worn, or broken.

What To Do If You Can’t Fix It – 5 Helpful Tips

You’re going to need to take action if you’ve tried all the options listed above and you still can’t get your filter to run. Here’s what you should do:

  • Aerate your aquarium water

Your aquarium is not going to crash instantly without a filter, although the situation can become more serious after a few hours.

In the meantime, use an air pump and air stone to oxygenate your aquarium water. This will help your fish breathe and supply dissolved oxygen to the beneficial bacteria that live within your substrate and on surfaces within the tank.

  • Run a spare filter

I recommend keeping a cheap spare filter for this kind of situation, but it’s very important to use it correctly here. If you’ve got an idea of how aquarium cycling and the nitrogen cycle work, you’ll know that special bacteria live in the media in your filter and that it can take several weeks to build up a decent colony.

Put the media from your faulty filter into your spare until you can get a new filter or fit replacement parts. You may have to trim the old sponge down to size, but that shouldn’t be a problem. Bio balls and other media types can also be transferred to your spare filter if the design allows custom media.

  • Buying replacement parts

You can usually buy replacement parts if you have a decent brand-name fish tank filter, although it may make more sense to buy a new filter in some cases. You can ask your local fish store to order replacement parts or simply purchase them online.

  • What if you don’t have a spare filter?

It is possible to care for the beneficial bacteria in your old filter media, although it can get a little messy if the old media hasn’t been rinsed in a while. Gently remove the media and place it in the tank near an air stone to encourage some water movement through the media and keep the good bacteria oxygenated until you can get a new filter up and running.

Note that if you purchase the same filter to replace your broken one, you can swap the filter media into the new filter. This will help prevent losses in the bacteria colony as the colony will still function in the new filter.

  • Running a second filter

Did you know that you can run two or even three filters in the same aquarium? Most aquarists will run a single powerful filter, although two smaller fish tank filters can provide adequate filtration while giving you that extra insurance in case one fails.

Understocking your tank and growing live plants are great ways to slow the build-up of nitrate levels in the long run, but you can also reduce your filtration needs by feeding your fish correctly. Uneaten food is a major cause of poor water quality.

Why isn’t my fish tank water filter working?

Fish tank filters don’t last forever, although you should get many years of use out of a quality product. The most common problems that affect aquarium filters are air locks, clogged media, clogged impellers, and power supply problems.

How do I know if my fish tank filter is broken?

Some fish tank filters are virtually silent, but all canister, hang on back, and internal power filters should create some flow from their outlet. Your filter is not working if it does not pump any water.

How do you unclog a fish tank filter?

Start by rinsing out your filtration media. I recommend rinsing your filter sponge and media in a separate container filled with aquarium water from a water change.

Some filter cartridges and floss cannot be reused once clogged, so remember to replace them on a regular basis. Your filter may have indicators that tell you when to service or replace media, but you can also look for guidance in your instruction manual or check with the manufacturer online.

How long can fish survive without a filter?

Your fish may survive hours, days, or weeks without a filter — it all depends on your aquarium size, fish species, stocking level, and water chemistry. You can keep your water safer for longer by running an airstone, reducing feeding, and by testing water parameters and performing water changes as necessary.

What to do if your fish filter stops working?

A malfunctioning filter will reduce water quality, so this is one problem you should attend to immediately. Take a few minutes to run through the solutions mentioned in this article, including checking the power supply and looking for obstructions and clogs.

If you can’t solve the problem, you’ll need to install a different filter. I recommend seeding the new filter media with bacteria from your old filter.

How do I know if my filter is working in my fish tank?

Adequate mechanical and biological filtration will keep your water clean and prevent odors. A working fish tank filter will suck water into its outtake tube and pump it back into the aquarium. This should create a gentle current that you can see, hear, or feel in the water.

Final Thoughts

Providing proper filtration is essential for maintaining a beautiful aquarium and healthy fish, so it can be pretty stressful when your equipment malfunctions. I hope the advice in this guide helps you fix your filter problems without ordering a replacement, but please keep safety in mind when inspecting electrical equipment.

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