Many new HOB filters (Hang On Back) that come with tank sets are very noisy when first used. It can take weeks for a bio-film to build up on the impeller and quiet the rattle. In some cases, especially with the cheaper models the tank never does stop being noticeably noisy.

The following post shows how to quiet your HOB filter for nothing more than the cost of a small jar of Vaseline.

Note the ingredient, no additives, menthol etc. added. You could possibly even use generic lip-balm if it has nothing more than petroleum jelly. It is inert for all practical purposes in a freshwater tank. I have no experience using this method on a marine system, so use at your own risk in a saltwater tank.

The first step is to pull the lift tube from the u-tube. If this is a filter that's been running a while it is also a good opportunity to give it a good scrub.

Once the lift tube is out the u-tube will pull out vertically, see the side view pic below to illustrate how the u-tube seats.

Simply pull upwards steadily until the u-tube comes free.

Once the u-tube has been removed you should see an impeller, they are typically green or white, but the color may vary and is unimportant.

Use a pair of needle-nose pliers, long tweezers or even chopsticks, pull the impeller from the housing. Pull straight up, but expect a bit of resistance from the magnet of the impeller and the drive coil.

Once the impeller is free wipe it down and remove any debris. this is not necessary with a new filter unit.

Using a small amount of Vaseline apply it evenly to the magnetic cylinder of the impeller.

Using the pliers, tweezers or chopsticks place the impeller back into the drive housing. Then, ensuring it is lined up, replace the u-tube over the impeller. There should be an alignment post or slot on the HOB filters body. Once it’s lined up it should seat easily and solidly.

Note the flow control on the u-tube. On occasion this will generate noise as bubbles of air slip by the seal and move through the impeller. This can sound like a can full of rocks if severe. By pulling the adjuster and liberally applying Vaseline around the seal this problem can be fixed as well.

Replace the lift tube. mount the filter on the tank and be sure to prime it before powering it up. A cup full of water should be enough to get it started.

You should now have a whisper quiet filter without spending a fortune on a high end brand.