How I Clean Aquaclear Hob Filters And Media


The AquaClear (also sold under Fluval brand) hang-on-back (HOB) filters are very commonly used and recommended on here. In my opinion, they are the best HOB filter on the market. This will be in-depth description of the media included with the filter, and a detailed “how-to” on how often and how I clean the media, and the filter itself.

Note: This is for the standard media that comes with the filter.
1. Sponge. This is the mechanical filtration that removes large pieces of debris from your tank. This includes things like food, poop, plant matter, or anything else floating around in your tank like pet hair, fish/snail eggs, even fish fry or shrimp that get sucked up. Because of the sponges’ job, it should be keep clean and clear so it can do its job the best without damaging the performance of the filter. I recommend cleaning the sponge weekly or bi-weekly. A well maintained sponge can last well over a year, sometimes even a couple years. If it stops coming clean, or is too clogged that it slows the flow even after cleaning, or degrades and loses its spongey ability (is that even a word?), you will need to replace it.
To clean the sponge…
· Use either old tank water or tap water.
· Squeeze the sponge over and over under the water. You can scrub it with your fingers gently if needed.
· Do this until it appears clean. Note: It will never be as white as it was when you first got it, so don’t get too frustrated if its “not coming clean”. You will be able to tell the difference of a dirty sponge and clean sponge.
· This will force out a lot of the dirt and gunk that is in the sponge. The better job you do with this, the longer it will last you and save you money on replacing it.
· If you are worried about using tap water and killing bacteria in the sponge, don't be. There is a much greater amount of bacteria in the Bio-max that can double in amount in 24 hours, to make up for any losses in the sponge.

2. Activated Carbon, aka charcoal. This is your chemical filtration. The job of this media is to extract toxins from the water. It will remove chemicals from your water until the carbon becomes exhausted. This media typically lasts 3-4 weeks and then should be replaced. It can be used for a total of 3-4 weeks with time out of the water not counting against it. Carbon can remove things like plant foods, trace elements, and mineral supplements from the water. For this reason, many hobbyists choose not to use carbon in their filters unless there is a precise reason to do so, like removing medications or to get rid of an odor in the tank. If your tank does not contain live plants, there isn’t much of a down-side to using carbon. As for cleaning it, because the carbon pieces are so small, the media bag used for the carbon doesn’t let much into it other than water. I recommend this to be cleaned weekly or bi-weekly as needed when you do your regular water changes. All you need to do is swish it around in either old tank water or tap water to remove anything that may be stuck to the media bag. When dosing any medication to a tank, you should remove your carbon or the carbon will remove the medication before the medication can help the problem you are trying to fix.

If you wish to use carbon and want to save some money, you can purchase reusable media bags and buy activated carbon in bulk. A half cup will treat 40 gallons for 3-4 weeks. You can use that ratio to calculate how much you need for your size tank. Using more than needed won't necessarily last longer. If you have extremely hard water, it may only last 2 weeks. After it is exhausted, empty the media bag, give it a good rinse and add the correct amount for your tank.

3. Bio-max. This is your biological filtration. The job of this media is to house beneficial bacteria (BB). The BB will convert ammonia molecules in the water to nitrite molecules as the water passes through the Bio-max. There is a 2[SUP]nd[/SUP] form of bacteria that will convert the nitrite molecules into nitrate molecules, which are far less toxic to your fish. Having a healthy population of both types of BB to keep the ammonia and nitrite levels at 0, is the goal, and means you have a cycled tank that is safe for fish to live in. This should be cleaned weekly or bi-weekly when you do your regular water changes. Unless damaged or contaminated, you should never need to replace the Bio-max. It will not degrade and under normal conditions, won’t get damaged.
To clean the Bio-max…
· Use only old tank water, tap water that has been treated with a product that removes chlorine, or tap water that has aged 24-48 hours. Chlorine will kill the bacteria, which will cause you to have to start the cycling process all over again.
· When you have your de-chlorinated water, all you need to do is swish it around in said water. This will cause any debris that is stuck to the Bio-max to fall off.

Cleaning the entire filter
A few of the reasons for why you should complete routine filter maintenance and cleaning are…
· A cleaner system will do the job better than a dirty one.
· Debris can get trapped in the filter. As it breaks down it can cause ammonia, nitrite, and nitrate molecules to increase, would could affect the water quality.
· Algae can live in the filter and filter tubes. Algae in itself is not necessarily bad, but it can be unsightly and affect any live plants you may have.
· Costs. The better you maintain the filter, the longer the media and filter will last you, saving you money. The savings by doing routine maintenance could pay for the filter within a year or two.

I will clean the entire filter once every 4-6 weeks. The following is a step-by-step guide on how I do this. To do this you will need a toothbrush that is new and will only ever be used with your tanks and filters; and a running faucet. A 5 gallon bucket will make it easier, but not necessary.

Disassembling from the tank procedure:
1. Unplug the filter.
2. Remove the intake tubes from the filter. Add them to the bucket if you are using it, or bring it to your sink.
3. Dump out some of the water from the filter into the tank so it is easier to carry without splashing over and making a mess.
4. Carefully lift the filter off of your tank without letting the plug get in the tank.
5. Place your Bio-max in the tank so it remains wet to preserve the BB.
6. Put the filter, media basket, and media in the bucket and bring it to the sink.

Cleaning procedure:
Section 1: Tubes
1. Separate the tubes into their pieces if not already done.
2. Under warm running water, use the toothbrush to clean out the inside and outside of the tubes and the ends where gunk gets trapped.
3. When you get to the U shaped piece, use the toothbrush to clean both vertical parts. Then run hot water through the pieces to loosen up anything stuck to the flat part you can’t reach with the toothbrush.
4. Fill the tube with enough water to fill the flat part between the open ends. Place both hands on the open ends to cover both ends and shake it vigorously to dislodge anything else that may be stuck in there.
5. Rinse and empty the tubes of water. Set aside.

Section 2: Media and Media Basket
1. Follow above recommended procedure for cleaning media
2. To clean the media basket/tray, simply run it under warm or hot water.
3. Use the toothbrush as needed to remove any stuck on gunk. Rinse and set aside.

Section 3: Filter Box and impeller
1. Run warm water to rinse out the inside of the box. Dump out the water and lose debris.
2. Being careful, yet firm, place 2 fingers under the grey piece where the intake tube enters the filter. Use your thumb to hold on to it and lift the grey pieces straight up. Do not lift too hard or fast because you may inadvertently break it.
3. Use the toothbrush to clean the underside of this grey piece. Rinse and set aside.
4. Grab on to the black housing under the filter that is attached to the power cord and give it a twist. This will remove it from the filter box.
CAUTION! You may want to insert a drain catch before doing the next step.
5. Pull out the fan like thing from the housing. This is your impeller which spins at a high rate of speed, drawing the water into the filter. Be careful not to drop it down the drain if you don’t have a drain catch.
6. Run it under the water to clean any gunk from it. You can use your fingers or the toothbrush if needed.
7. You can run the housing under warm or hot water to get any gunk that settled in there. After you are satisfied with its cleanliness, replace the impeller, dry the cord if it is wet, and set aside.
8. Use warm or hot water and toothbrush to scrub the inside and outside of the filter box to get anything else that may be stuck on.
9. When you are satisfied with how clean it is, you can reassemble the filter
10. Replace impeller housing.
11. Replace un-named grey piece until it snaps in firmly.
12. Replace tubing so it fits snugly in place.
13. Replace media basket and media.
14. Make sure the plug and cord is dry to avoid electrocution.
15. Re-hang the filter on the tank, add the Bio-max to the filter, and fill the filter with water from the tank.
16. When the water in the filter overfills, it is full enough and when you are ready to, plug the filter back in.

The whole process might take longer the first couple of times, but when you get in a routine of doing it, it will only take 10-20 minutes, depending on size. It is easy to do and will save you lots of money.

Other options for filter media:
-Filter floss, polishing pads
-More Bio-max, or other biological filtration media
-3rd party products like Seachem Purigen, API Ammo Chips/Ammo Carb, etc.
Because of the media basket style of these filters, they are highly customize-able to fit your needs, if it fits in the basket, it will work in the filter.

Thanks for reading this and I hope it was helpful to you.


SWEET Thread, thanks for going into detail off of my thread about this earlier. Please sticky this!

Also, is it ok to clean the sponge, carbon and biomax at the same time? how easy does the biomax keep the bacteria on when swishing it through tank water? What option are there to replace the carbon since my tank is heavily planted and I use Flourish and Excel? Maybe more biomax?

Thanks and maybe can add this into the already amazing article



Nice job there but my gosh ..... I haven't done that much work combined on four HOB's (two c3's, an ac50 and a C4) in two years. None have been cleaned or taken apart since new. I just replace the mechanical media monthly and the Purigen twice a year. And my water is crystal clear and sparkly.

Post #4 here:

My mechanical media is 8 months old and still works like new. My Purigen is 6 monthsold, and I regenerate it every 2-3 months, which costs me next to nothing but a little bleach and Prime. I'm sure the money I will save in 2 years of you replacing the media, will pay for the filters. That's why I do it.


This is so, so helpful. I have always been intimidated about cleaning my AquaClears; now I think I can do it. Thanks, alink!

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