Fluval 306 Canister Filter Troubleshooting

Filter is not pumping (taking in and pushing out water)

If the intake or outtake hose have any loops then the pump may not start. Make sure to shorten the length of the hoses where the intake hose is below the water and the outtake hose is just above the water.

Make sure filter’s power cord is unplugged from the electrical outlet. Prime the filter by pumping the instant-prime handle (the little nob next to the AquaStop valve). The canister should start to fill with water. Stop pumping the instant-prime handle once you hear water continuously flowing into the canister. Once the canister is full, plug the device’s power cord back in.

Check the intake hose and make sure the canister is completely closed. Any leaks or holes will cause the filter to slow down or stop pumping water. Pinprick holes or holes that cannot be seen can occur. Consider changing the intake hose.

Water coming out of the outtake has slowed down

Check and clean the sponge. If sponge is not dirty then change the filter media as the media may be too dirty to allow proper water flow. Remember do not change all the filter media as this will kill the beneficial bacteria and you will need to cycle the tank again.

Check two things, make sure there is no aeration device such as a bubbler near the intake hose and make sure there is no debris blocking the intake

Check the intake hose and make sure the canister is completely closed. Any leaks or holes will cause the filter to slow down or stop pumping water. Pinprick holes or holes that cannot be seen can occur. Consider changing the intake hose.

Water keeps leaking from the canister

Check the seal ring for dryness, cracks and debris as both will break the airtight seal. If dry and void of lubrication without cracks and malformation, reapply silicon lubricant. Do not use Vaseline as it will not allow for a proper seal and will lead to leaks.

Reseat the lid to make sure it is sitting properly on the base before locking it into place

The water becomes dirty quickly even after water changes

Check the sponge first. If it is dirty rinse out with tank water. If this does not solve the problem then change the filter media. Remember do not change all the filter media as this will kill the beneficial bacteria and you will need to cycle the tank again.

Make sure that the filter is pumping water properly. If not there may be a blockage in the intake/outtake or the filter may need to be primed again.

Each model has a limit on what size tank they are built for. The 306 model is made for 70 gallon sized tanks or less.

Filter is making strange noises

Check the impeller for debris or damage, reseat the impeller and its cover if not damaged. Replace the impeller if damaged.

Check the intake to make sure it is not taking in air and debris such as sand and substrate.