Fluval FX6 Air Trapped

Fluval FX6 Air Trapped

Fixing issues that arise in your aquarium is part of being a good aquarist, but when your canister filter is on the fritz, it can be hard to figure out what to do. Here’s how to deal with air trapped in your Fluval FX6.

Issues with the FX6 canister filter can be caused by malfunctions in the O-rings, pump, and impeller. The issue can be resolved by adjusting the amount of filter media and readjusting the position of the hoses.

There are a lot of things that can go wrong with a Fluval FX6 canister, and troubleshooting can be tricky if you don’t know what you’re looking for. The rest of this article will walk you through common problems with the Fluval FX6 canister filter and how to fix it.

What Causes Trapped Air in a Fluval FX6?

If you have a Fluval FX6, you may notice that about every 12 hours when it shuts off to purge, a lot of trapped air releases. Oftentimes, this isn’t anything to worry about if it doesn’t seem to be affecting performance. Trapped air can be a result of cavitation, the formation of an empty space or cavity, in a solid object.

This occurs naturally within the design of the FX6 and can be a nuisance. A possible cause of cavitation is if there’s not enough flow back to the return pump due to older filter media (or too much). Lastly, trapped air in the FX6 can be caused the way the hose is set up. If the inlet run creates too much resistance, it can cause a drop in pressure on one side of the return pump.

Put simply, if your hoses are on backwards, a drop in pressure can occur that allows air bubbles to build up in the canister.

How Do You Get Trapped Air Out of Fluval FX6?

Fixing these issues can be a nuisance, but thankfully, there are some straightforward ways to troubleshoot issues with your FX6. First, check your intake hoses to make sure they are installed correctly according to the assembly instructions.

Remember, if they are the wrong way around, cavitation can occur, trapping air in the canister and reducing its effectiveness. Make sure your intake is short with no slack loops and travels straight from the canister to the tank. Use the longer hose as the return for the opposite side from the intake.

Why Is My FX6 Filter Making a Noise?

The FX6 is an enclosed system that will make noise if air escapes, parts are grating against one another, or the motor is running choppy. It’s important to investigate the cause of a noisy FX6 because the issue is often with the motor, which can be expensive to replace.

After a cleaning, you might find that your impeller has a hard time starting and makes noise. Cleaning the inside and removing all of the filter material to clear out trapped debris and sand will help. Media stuck in the pump can also cause a noisy canister, so try opening up the pump and removing anything jamming it.

After reassembling, run the filter again to see if everything is running properly. Trapped air can also cause noise in your Fluval FX6, which isn’t problematic as long as it isn’t affecting your filter’s performance.

They need to turn off for about 10 minutes every 24 hours to clear out trapped air and run properly. Removing some filter media can also help reduce issues with bubbling.

How Do You Prime a Fluval FX6?

One of the best parts about the Fluval FX6 is that it can be self-priming; however, you’ll need to prime it manually when you first set up. First, remove your filter media from the filter to check for additional parts stored in the filter.

Place the filter close to the aquarium and set up your hoses. Once your filter is in position, fill it with 6 liters of water, allowing self-priming to begin, and just like that, you’re all set!

Troubleshooting Other Fluval Canister Filter Issues

There are several other issues that might arise during the lifespan of your canister filter, including issues with the O-rings, impeller, hoses, and motors. The best way to reduce potential issues with your canister filter is to make sure you maintain it well.


Make sure to take care of your hoses and ensure that they don’t get clogged with debris. Ideally, you should clean them out three times per year. The hoses should never be bent, looping, or kinked either for best results. Silicone lubricant is a good idea after any maintenance to help prevent leaks.

Lastly, depending on the age of your impeller, it might be wise to replace it. If you’re noticing any vibration or shuddering noises from the impeller, you’ll want to replace it. When you buy a FX6, it comes with a replacement impeller box, so make sure to set it aside to install when your old one needs replacing.

Common Issues

If your FX6 won’t start, it’s likely because the impeller is jammed or media is stuck in the pump. To rectify this, clean the inside of the canister and remove your filter media so that you can clear out any trapped debris. Once done, reassemble and run the filter again to see if the issue is resolved.

If you’re having issued with reduced flow, check once again that there is no blockage in the impeller or clogs in your hose. You may also have simply used too much media and need to reduce the amount you’re using.

Final Thoughts

There are a lot of issues that can arise with the FX6 canister filter, but one of the most common annoying issues is when air gets trapped in the filter. Unfortunately, this is a natural part of the filter cycle and is part of the reason that the filter needs to turn off at least every 24 hours to purge excess air.

Cleaning and maintaining your canister filter regularly can help prevent cavitation and other issues from arising in your Fluval FX6 canister filter.