Important: Disconnect mains electricity supply before handling or attempting maintenance. Always fully read and check the troubleshooting section within your product instruction manual.
Please ensure the impeller underneath the guard on the underside of the motor head is not blocked, clogged, damaged or unseated in anyway. Ensure that the plastic propeller part of the impeller is attached to the magnetic body part and that they have not come apart or split. If these parts looks fine and there are two rubber grommets fitted on each end of the shaft, or
If your external filter seems to have a reduced flow rate, don’t worry — this is usually straightforward to fix. Follow the steps below to identify and resolve the issue.
Safety First
Before doing anything:
Unplug the filter from the mains electricity.
Read the troubleshooting section in your product instruction manual to familiarise yourself with your filter’s components.
Step 1: Check the Impeller (the heart of your filter)
The impeller is the small spinning part that moves the water — and if it’s not working properly, the whole filter can struggle.
To check it:
Locate the impeller beneath the guard on the underside of the motor head.
Remove it carefully and check:
Is it clogged with debris or algae?
Has it become unseated or moved out of place?
Is the plastic propeller still attached to the magnetic body? (They sometimes separate or split.)
Are the rubber grommets (small black rubber ends) still fitted on both ends of the impeller shaft?
If everything looks intact, gently reassemble the impeller and return it to the filter.
Step 2: Check the Filter Trays
Open the canister and ensure the trays are not overfilled with media.
Overpacking can restrict water flow and cause the filter to work harder than it should.
Step 3: Check All Pipes and Connections
Go through this checklist one by one:
Are the green plastic pipes connected properly, with screw-heads tightened?
Are the tap connections fitted securely at both ends?
Is all black pipework submerged inside the aquarium?
The water level in your tank must be high enough to completely cover both the inlet and outlet pipes, including any joints.
Is the tap fully inserted into the filter and locked into place before you open it?
Are the green pipes as straight as possible, with no tight bends or kinks that could restrict flow?
Step 4: Prime the Filter Properly
Priming fills the filter with water and starts the flow.
How to do it:
Fill the filter canister as high as possible with aquarium water before starting.
Place the filter under the tank (gravity helps it work).
Firmly press the large priming button on the filter several times.
Watch the pipes:
You should see water start to move through them.
Place a finger under the black inlet pipe in the tank to feel for suction.
Keep pressing the plunger until the water flows steadily — this may take several firm pumps.
Once water begins moving and filling the pipes, the filter should start up and run normally.
Still Need Help?
Watch our step-by-step video guide:
Final Tip:
If you’ve followed all these steps and the flow is still low, consider checking:
Whether the impeller needs replacing.
If the hoses need cleaning (internal build-up can reduce flow).
If the filter has been running for several months without maintenance — it may be time for a full clean.