Why Is My Aquarium Filter Not Working? Common Fixes

The short answer: Your aquarium filter is likely not working due to a clogged intake or filter media, a broken impeller, or an air lock. Check the intake tube, clean or replace the media, and ensure the impeller spins freely.

1. Check for a Clogged Intake or Output

One of the most common reasons a filter stops working is a blockage in the intake tube, strainer, or output nozzle. Debris, snail shells, or plant leaves can restrict water flow, making the filter seem dead but actually just struggling.

How to fix:

• Unplug the filter and remove the intake tube and strainer.
• Rinse them under warm water, using a soft brush or pipe cleaner to dislodge any gunk.
• Check the output nozzle for buildup, especially if you have hard water (calcium deposits).
• Reassemble and test the filter in a bucket of water before returning it to the tank.

If the filter still hums but no water flows, the blockage might be inside the impeller housing.

2. Clean or Replace the Filter Media

Filter media (sponges, cartridges, bio-rings) can become clogged with fish waste and debris over time. A thick layer of sludge restricts water flow, reducing filtration efficiency. While it’s tempting to replace media often, doing so can remove beneficial bacteria. Instead, clean it properly.

How to fix:

• Turn off and unplug the filter.
• Remove the media and rinse it in a bucket of dechlorinated water (never tap water, as chlorine kills bacteria).
• Squeeze sponges gently to release trapped debris, but don’t wring them dry.
• If the media is falling apart or clogged beyond cleaning, replace it. For cartridges, replace every 2 to 4 weeks, but keep a spare in the tank to preserve bacteria.
• For canister filters, clean the media every 3 to 6 months, but stagger cleaning to maintain beneficial bacteria.

3. Inspect the Impeller and Drive Unit

The impeller is the spinning part that pulls water into the filter. It can get jammed with debris, hair, or even a small snail. If the impeller is broken or worn, the filter will hum but not push water.

How to fix:

• Unplug the filter and open the impeller housing (usually accessible from the bottom or side).
• Remove the impeller and its shaft.
• Clean both with a soft toothbrush and warm water, removing any tangled material.
• Check for cracks or wear on the impeller blades. If damaged, order a replacement part (most brands sell them online).
• Lubricate the shaft with a bit of petroleum jelly (food-grade silicone grease is better) to ensure smooth rotation.
• Reassemble and test.

4. Eliminate Air Locks

An air lock occurs when air gets trapped inside the filter, preventing water from being pulled in. This is common after cleaning or when the water level drops too low.

How to fix:

• Prime the filter: fill the filter chamber with tank water before plugging it back in.
• Tilt the filter slightly while running to help air escape.
• For canister filters, use the prime button or pour water into the intake hose until it flows out.
• Ensure the water level in your tank covers the filter intake completely. If the water is too low, the filter may suck in air.

5. Verify the Power Supply and Electrical Issues

Sometimes the filter isn’t working because it’s not getting power. Check the outlet, the power cord, and the adapter (if any). A tripped GFCI or a blown fuse could be the culprit.

How to fix:

• Plug the filter into a different outlet to rule out a dead socket.
• Inspect the power cord for frays or cuts. If damaged, replace the filter or the cord.
• If you use a timer or power strip, test the filter directly in a wall outlet.
• For external filters, check that the pump is properly seated and the connections are secure.

6. When to Replace the Filter

If you’ve tried all the above and the filter still doesn’t work, it might be time for a new one. Most filters last 2 to 3 years, but wear and tear can shorten that. Also, consider if your filter is undersized for your tank. A filter rated for a smaller tank will struggle to keep up, leading to constant clogs and poor water quality.

Signs you need a new filter:

• Motor burns out (smell of burning plastic).
• Impeller replacement doesn’t restore function.
• Filter is more than 5 years old and performs poorly.
• If you’re upgrading your tank or fish load, a new filter with a higher flow rate may be necessary.

For a comprehensive look at the best filters available, check out our Best Aquarium Filters 2026: Top 10 Compared guide.

Frequently Asked Questions

Q: Why does my filter make noise but not pump water?
This usually indicates a clogged impeller or an air lock. Unplug the filter, clean the impeller, and prime the filter to remove air. Also, check that the water level is high enough.

Q: How often should I clean my aquarium filter?
Every 2 to 4 weeks for sponges and cartridges, and every 3 to 6 months for canister media. Rinse in dechlorinated water to preserve beneficial bacteria. Replace cartridges monthly.

Q: Can I turn off my aquarium filter at night?
It’s not recommended. Filters provide essential aeration and biological filtration. Turning it off can cause oxygen depletion and a buildup of ammonia. Keep it running 24/7.

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