How do You Clean a Hang On Back Filter?

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The Hang On Back (HOB) filter is the most popular option among aquarists for good reasons. It’s easy to install, maintain, and has virtually zero downsides.

However, just like any other filtering system, this also requires regular cleaning and maintenance. It’s important to do it properly since a lot can go wrong, even with the simplest tasks.

Cleaning the aquarium filter is especially a volatile area that many novice aquarium keepers tend to make worse.

The most common mistakes novice aquarium owners make when cleaning the filtering system include:

  • Overcleaning – They tend to be so thorough about the cleaning process, destroying the cultures of beneficial bacteria inhabiting the filter. This results in the cleaning process doing more harm than good.
  • Using chemicals – The same thing applies. Many cleaning chemicals are toxic for the filter’s beneficial microbiome. Relying on chemicals to clean and sterilize the filter will backfire, disrupting the tank’s healthy microfauna.
  • Not cleaning it regularly – A dirty and clogged filter will result in poorer water conditions, affecting your fish as a result. Many people tend to ignore the filtering system during the maintenance phase, ultimately putting their fish’s lives at risk.

Let’s see how you optimally perform the cleaning process for the best results.

Cleaning a Hang On Back Power Filter

The cleaning process relies on several crucial steps:

  • Disconnecting the filtering system – This may sound as a given, but you would be amazed at how many people skip this step by accident. Disconnecting the filter is essential since working with water near an electrically-powered device is never wise.
  • Have a bucket of water ready – The bucket needs to contain water aquarium water. Don’t use tap water since all tap water contains chlorine. This is a chemical that sterilizes the water, making it safe for human consumption. As a result, chlorine will eliminate all beneficial bacteria inhabiting the filter, doing more harm than good in the process. Using tank water will prevent that and preserve beneficial bacteria cultures that will stabilize your tank’s microbiome.
  • Clean or replace the carbon filter media – If the filter media is clogged beyond cleaning, simply replace it. Otherwise, it will fail at performing its intended task. Also, clogged and non-functional carbon filters will harbor decaying matter and cultures of harmful bacteria that are a detriment to the aquatic environment.
  • Remove algae deposits – Make sure you clean visible traces and deposits of algae, but don’t go overboard with it. Algae are generally an asset for any aquatic environment in controlled amounts. They only become a problem if growing beyond control to overtake and suffocate the habitat.
  • Clean the new filter media with tank water – Doing so will imbue the new filter media with the beneficial bacteria in the water tank. It will also balance the filter’s chemistry to match that in the tank water.
  • Mount the filter back into its place – Once the cleaning is complete, mount the filter back into the tank, fill it partially with some tank water, plug it in and turn it on.

At this point, the cleaning process is complete. It’s not a demanding process, and it’s necessary to keep your fish’s environment healthy and thriving.

How Often To Clean the HOB Filter?

Unlike canister filters that can go 4 months without any cleaning, HOB filters require more frequent maintenance. Ideally, you should clean a HOB filter every 2-3 weeks, even more often if necessary.

In some cases, you may need to clean the filter weekly, especially if you have an overcrowded tank that gets messy fast.

Some of these cases include:

  • An overcrowded tank – Having more fish in the tank than you should, could backfire soon. The excess fish will produce more waste which will mix with food residues and dead plant matter to clog the filter and increase ammonia levels in the tank.
  • A fine-grained substrate – The filtering system will also suck in substrate particles if they’re fine-grained and light enough to float towards the filter. Sand substrates tend to fall into this category. It’s not absolutely necessary to clean the filter if you have a sand substrate; it just makes it more likely.
  • Algae overgrowth – Not controlling the algae in your tank may cause problems along the way. Algae can spread fast under the right circumstances, aka having proper lighting, low food competition, and no algae-eating tank inhabitants to control their number. In this case, algae can flood the filter, reducing its effectiveness and even clogging it.
  • Having several scavenger creatures – We include here snails and scavenger fish that lurk on the substrate. These creatures, especially if they’re big enough, will ruffle the substrate, filling the water with particles and creating a cloudy effect. These particles will accumulate in the filter, reducing its overall performance.

So long as you avoid these situations and maintain your tank properly, your filter will do fine with rarer cleaning. Once every 3 weeks should do.

How Long Should Filter Media Stay Out of Water?

The filter media is the breeding ground for beneficial bacteria. These aerobic microorganisms (bacteria that thrive in oxygenated environments) require water to remain alive. While they can withstand some time out of water, they will usually start dying off after 2 hours of no moisture.

In many cases, the bacterial cultures will go away completely within 24 hours out of water. So, make sure that doesn’t happen since merely lacking a proper aquatic environment will essentially sterilize the filter.

If you have power outages that last more than 2 hours, make sure the filtering system remains humid. You can either submerge the filter media in tank water or pour water over it regularly to keep the bacterial cultures alive.

How Often Do You Replace the Filter Media?

How often you need to replace the filter media depends on several factors, namely:

  • First, how often you clean the tank and perform water changes
  • How crowded the tank is
  • And how often you clean the filter, etc.

The type of filtering you’re using is also crucial here. There are 3 primary filters that most aquarium owners will use:

– Mechanical Filters

Mechanical filters rely on foam or sponges to trap debris. Their cell size and gaps can vary, as part of different filtering types, each effective for various sizes of debris.

Mechanical filters effectively combat water waste and can handle impressive loads over time. You can clean the sponge regularly to ensure it operates at maximum efficiency, but you need to change it after some time.

Changing the sponge filter media every 6 months would be ideal to ensure its effectiveness. Most sponges will begin to deteriorate after that timeframe.

– Chemical Filters

These filters typically rely on carbon filter media to trap heavy water metals and toxic impurities that can contaminate the aquatic environment. Carbon filters are among the most reliable devices, keeping the water clean and pure and creating the ideal environment for your fish.

The problem with carbon-based filters is that they often get saturated with debris and impurities, lowering their effectiveness dramatically. These filters may also become a breeding ground for harmful cultures of bacteria that may affect your fish population.

I recommend changing the carbon filter media monthly or upon completing specific tasks. These include cleansing the water of certain medications or cleaning heavily murky or cloudy waters resulting from algae overgrowth, unclean tanks, or other sources.

– Biological Filters

Biological filters are usually the byproduct of the aquatic environment. These filters basically occur naturally, defining the process of bacterial formation inside conventional mechanical filters.

These cultures of beneficial bacteria will form inside the filter media and the filter housing and multiply consistently over time. I cannot overstate the role of beneficial bacteria in stabilizing the tank’s ecosystem. These microorganisms consume the nitrogenous waste resulting from fish poop, converting it into easily digestible forms by other microorganisms.

This makes these bacteria essential to ensuring a healthy and stable environment for your fish.

The problem is that the beneficial bacteria thrive in maintained mechanical filters with free-flowing currents. Clogged filters will hurt them, which is why proper filter maintenance is ideal for supporting the colony of beneficial bacteria.

Mechanical filter media tends to lose its effectiveness at around the 6-month mark, at which point changing the media is necessary. I suggest cleaning your filtering system regularly to monitor its composure and effectiveness and understand when the time has come for replacement.


The filtering system is your tank’s respiratory system. If it’s in good shape, the tank will ‘breathe,’ keeping the fish in peak condition throughout the year.

If you have a HOB filter, clean it regularly, as I’ve shown in this article, to keep your fish population safe and thriving.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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