A working filter is the heart of your aquarium. It keeps the water clean, removes waste, provides oxygen, and keeps fish healthy. But sometimes the filter suddenly stops, becomes slow, or makes strange sounds. When this happens, it can worry beginners—especially when fish start acting stressed.
The good news? Most filter problems are simple to fix. In this guide, you’ll understand the common reasons why an aquarium filter stops working and how you can solve each problem easily at home.
1. The Filter Is Not Getting Power
The most common reason for a filter not working is simple—there is no electricity reaching it.
✔ Quick Checks:
Make sure the switch is turned on.
Check if the plug is loose.
Change outlets to determine if the outlet is working.
Check for Damaged Wires
If you use an extension board, test the filter directly in the wall outlet. Sometimes extensions become faulty.
2. The Motor Is Jammed
Over time, dirt, sand, and debris can get inside the motor. This stops the impeller (the small spinning part) from moving.
✔ Signs:
Filter buzzing not pumping
No water flow
Filter vibrates
✔ Fix:
Switch off the filter
Open the motor section
Carefully remove the impeller.
Clean the impeller and its chamber with a soft brush.
Rinse everything in tank water-not tap water
Reassemble and turn it back on
If your filter uses magnets, they can sometimes stick. Cleaning usually fixes it.
3. Sponge or Media Is Completely Blocked
Filters collect dirt every day. When the sponge or media becomes too dirty, water stops flowing through it.
✔ Signs:
Very weak water flow
Water spills from sides instead of the outlet
Tank water seems cloudy
✔ Fix:
Remove the sponge or media
Squeeze it gently in old tank water.
DO NOT use tap water- kills beneficial bacteria
Put the sponge back
Cleaning once every 2 weeks keeps your filter running smooth.
4. Air Pump Not Functioning For Sponge Filters
If you use a sponge filter, its power comes from an air pump. If the pump stops, the sponge filter stops too.
✔ Check these:
Is it a noisy pump?
Is the air pipe bent, blocked or leaks?
Is the air stone plugged?
✔ Fix:
Replace the old air stone
Straighten or replace the pipe
Clean air inlet for the pump
Trying to raise the pump above water level can prevent backflow.
Air pump problems are almost always with the pipes or stones.
5. The Filter Needs Priming
Some filters (especially HOB and canister filters) need to be “primed” before they start working.
✔ When priming is required:
After cleaning the filter
After a power cut
Assembling the filter for the first time
✔ How to prime:
Fill the filter chamber with water
Make sure all pipes are filled with water
Filter start
If still filtering problem persists, refill and try again.
6. Impeller Broken or Worn Out
If the impeller becomes broken, the filter no longer can pump well.
✔ Signs:
Loud rattling noise
Low flow even after cleaning
Filter starts then continually cuts out
If cleaning doesn’t help, you may need a new impeller. They are cheap and easy to replace.
7. Too Much Junk in the Filter Tubes
For HOB and canister filters, pipes get dirty inside. This prevents the flow.
✔ Fix:
Use a pipe cleaning brush
Rinse pipes with warm, not hot water
Reattach and test the flow
Cleaning your pipes every 1–2 months will help maintain a strong flow.
8. Wrong Filter Size for Your Tank
Sometimes beginners buy a filter that’s too weak for their aquarium size.
✔ Signs:
Water is often turbid
Filter struggles even when clean
Fish behave stressed.
✔ Solution:
Select a filter with correct output:
Small tanks 20–40L: Sponge filter or small HOB
Medium tanks 60–100L: Larger HOB or canister
Large tanks: Canister filter only
A good filter keeps your tank healthy and stable.
9. Airlock Inside the Filter
Sometimes air gets trapped inside the filter, especially after cleaning.
✔ Signs:
Filter runs but makes gurgling noise
Water flow is slow
Water starts and stops incessantly.
✔ Fix:
Tilt the filter slightly
Allow any trapped air to escape
Start again filtration
This often resolves it on the spot.
10. Mechanical Failure
If none of the above works, the filter may be old or damaged internally.
✔ Signs:
No sound
No vibration
Burning smell (rare but serious)
If the motor is burnt, replacement of the filter is the safest option.
Final Tips to Keep Your Filter Healthy ⭐
Clean the filter sponge every 2 weeks
Never wash media with tap water
Not to let the filter get dry.
Keep the filter running 24/7 Replace broken parts immediately A clean, working filter = healthy water = happy fish.