What’s the Best HOB Filter?

There are many different HOB (hang on back) filters on the market. And as long as you choose one that is rated high enough for the size and stocking density of your fish tank, you probably wouldn’t go wrong by selecting any one of them in particular. But some people won’t settle for anything other than the best HOB filter, and that’s exactly why we’ve created this page.

Throughout this article, we are going to explain which 3 HOB filters we find to be the best, the features of each one, where you can purchase them, how to set them up, and how to perform the proper maintenance for each one – everything you’ll need to succeed.

The filters that we are going to recommend aren’t specific models (ex: AquaClear 70, Marineland Emperor 400, Fluval C2) because, as mentioned earlier, the exact model of each brand that will work best for you will depend on what size of tank you have, how strong of current your particular species of fish enjoy, and how stocked your fish tank is. Instead, this article will include which overall brands we rank to be the best. After you understand the features, pros, and cons of each one, then it just comes to selecting the appropriate model/size of that brand’s product line and you’re good to go.

There’s a lot of information for us to cover, so let’s jump right into things, starting with the best HOB filter.



With AquaClear HOB filters, things are pretty straight forward for all model sizes (there’s the 20, 30, 50, 70, and 110). Essentially, a rotating impeller sucks water up the intake tube, over the wall of the aquarium glass, and down into the bottom of the filter casing. As the water level then rises up within the filter casing, the water is inevitable moved through a 3-stage filtration process, then overflows and drains back into the aquarium.

At the bottom of the filter casing, the first thing the water passes through on its way back to the aquarium, is a rectangular sponge. On top of that, is a bag of activated carbon (AKA charcoal), then a sack of biological filter media tops off the stack. The sponge captures all the debris and stops it from re-entering the aquarium or clogging the following filter medias. The activated carbon removes any medication, tannins (which make the water turn a yellowish tinge), and odors from the water. The biological media is very porous by nature, thus enabling it to house a large percentage of the beneficial bacteria in your aquarium that convert toxic ammonia and nitrite to nitrate, ensuring the water is safe for your fish.

The nice thing about this particular HOB filter is that all of these filter medias (the sponge, carbon, and biological media) are all stacked nicely in a basket. This makes cleaning the media (which we’ll discuss later) a much easier process in comparison to other HOB filters. You can literally remove all the media from the filter casing with just one hand.

Another thing that makes the AquaClear HOB power filters special in comparison to many other similar filters on the market is the fact that it has a feature to adjust the flow of the water. On top of the intake tube, there is a little knob of plastic. By grabbing hold of it and sliding it to the right, the water flow is decreased. This makes the entire filter much more versatile. For example, if you want to put it on a different-sized aquarium, you can, without it causing too aggressive of a current. Or if you notice that your fish prefer having a more stagnant environment, you can grant them with that. Or if you notice that your live plants are being pushed down in your aquarium from the current generated by the water flowing back into the aquarium from the filter, instead of having to relocate the filter or the plants, just slide the knob to the right and voila. It’s a great hang on back filter for planted aquariums.

One last thing worth noting about this filter is the warranty on them. According to the Hagen website, “AquaClear Power Filters are guaranteed against defects in material or workmanship under normal aquarium usage and service for as long as you own the filter.” They do specify that it is only for non-replaceable parts, so don’t expect them to replace the activated carbon that comes with the filter every few weeks/months when it wears out. And they do also state that the impeller isn’t covered by this warranty too. Nevertheless, if your filter quits on you at any point, just contact them and they’ll repair or replace it, free of charge.

Please note that this is the guarantee as of the date we published this article. Visit the Hagen website and review their warranty before contacting them about it.

Order an AquaClear HOB Filter

As mentioned earlier, there are several different model sizes for this filter. There’s the 20, 30, 50, 70, and 110. As you go up in numbers, the filter will process more water per hour and will make a stronger current on the outflow of the water. Make sure that you purchase the one that’s best suited for your aquarium in regards to its size, stocking density, and the amount of current that you’re after.



We rate the Fluval power filters (models C2, C3, and C4) as the second best HOB filter on the market. These ones work a little bit different than the famous AquaClear filters. Instead of having a bottom-up design for the water to flow through the filter media, they operate with the water mostly going back-to-front before re-entering the aquarium. It’s not a huge downfall by any means, but it is believed that filters with a design like this have a greater chance of water bypassing the filter media and just re-entering the aquarium without being filtered, although this isn’t definitive.

These filters have the same feature to control the water flow as the AquaClear HOB filters do, and they also have some other cool features as well. Most notably, they are deemed a 5 stage filter. Now that may sound a little funny because traditionally there are only 3 stages of filtration in an aquarium (mechanical, chemical, and biological), so you would assume that they added another 2 stages of something. But what they really did is design it to include 2 stages of mechanical filter media throughout the filtration process, and 2 stages of biological filter media.

First, after the water is pumped in through the intake tube and into the rear of the filter cavity, the water meets it’s first filtration media, a coarse, porous sponge. Just like with the AquaClear filters, this sponge catches debris before the water reaches the second stage of filter media. On the other side of that sponge is where the second stage of filter media is, and it’s actually another sponge. This second sponge is a lot finer than the first one, so its purpose is to catch all of the smaller debris that managed to get through the first, coarser sponge.

Now that the water has been ripped of its debris with the 2 stages of mechanical filtration, the next step in the process is for the water to pass through a compartment of activated carbon. Again, this removes any medication, removes any yellow-ish color, and removes any odors in the water. After this point, the water passed through the final compartment, a small basket filled with biological filter media, then re-enters the aquarium out the front of the filter.

So if you were counting along, that is a total of 4 stages of filtration. The 5th stage is actually pretty interesting, and something I haven’t seen on any other HOB filter before. As the water passes through the 4th stage, some of the water is actually re-routed up through a spout, and poured overtop of the basket containing the biological media of the 4th stage. On top of this basket is a thin piece of material that is very porous, thus allowing a large colony of beneficial bacteria to grow. This is the only stage of filter media that is above the water line inside the filter cavity. Being exposed like this gives it the ability to be in contact with a much higher concentration of oxygen than that is inside the water. As such, it boosts the number of beneficial bacteria that can grow on it, and that bacteria isn’t competing for the same oxygen that the fish in your aquarium are. It’s pretty neat.

After it passes through this oxygen-rich, porous, material, the water rejoins the rest of the water on its journey through the 4th stage of biological filter media as it makes its way back into your aquarium.

Aside from having the most stages of the filtration in comparison to any other of the 3 best HOB filters, this filter has some other cool features to bring up. When you look at the plastic piece that holds the first and second stage of filter media (the coarse and fine sponge) together, it has a little piece on the top that raises if water is flowing overtop of the sponge and not actually flowing through it. What this means is that if you see that little piece raised, you know that your sponges are quite clogged and need a good cleaning.

Fluval actually designed the intake tube quite innovatively as well. Instead of just connecting it together in a fixed position, the lower portion of the intake tube is slightly thinner than the upper portion, and it’s covered in ribs. To put the two pieces together you just shove the lower, thinner portion inside the upper, wider portion and it will click into place on the ribs. If you want the bottom of the intake tube to be a little higher in your aquarium, either for preference, or because you have a shallow aquarium, just shove the lower portion deeper into the upper portion and it will click into place along one of the many ribs.

Order a Fluval HOB Filter


Marineland Penguin/Emperor

We’ve rated Marineland’s Penguin and Emperor HOB filters 3rd best because there is quite the mixed opinion on them among fishkeepers. Some people swear by them, and some people swear at them.

The biggest selling point for these filters is the fact that they have bio-wheels, which are fibrous wheels that rotate and skim on the surface of the water as the last stage of filtration before the water returns to the aquarium. These things act just like that thin, porous material on top of the basket holding biological filter media for the Fluval HOB filters. They aren’t submerged in the water either, so they provide a great place where beneficial bacteria can grow in the presence of atmospheric oxygen and not take the oxygen that your fish are already competing for. Most of the sizes of these filters come with only one biowheel, but if you go with either the highest rated version for each model (the Marineland Emperor 400 power filter or the Penguin 350), you’ll actually get two biowheels. That means twice the oxygen-rich breeding grounds for beneficial bacteria to grow and establish.

The second thing that we really like about these filters is the fact that the intake tube has two different options for water to flow into. If you look halfway up the intake tube, you’ll see a little grey switch that rotates. This plastic piece can be pushed down and it will act just like any of the other HOB filters we’ve discussed, or it can be pushed up and it will expose a second entry way for water. Exposing the second entry way allows for greater water circulation in your aquarium and can help reduce “dead spots”, where water doesn’t flow and debris gathers. It’s a nice feature, however, the little grey plastic piece that your push up and down can be an eyesore if you’re like me and want to keep the focus on the fish and decor of your tank, not the equipment. Luckily, the piece comes off pretty easy, so don’t worry about it too much if you plan to have it open all the time.

The third thing we like about the Marineland Penguin and Emperor HOB filters is the fact that the intake tube can be easily trimmed, either if you prefer your filters to be a little higher than usual, or your just want to put the filter on a tank that’s a little shallow. Use a hacksaw and she’ll come off just fine. Don’t worry if where you cut it off looks a little haggard. There is a piece that goes onto the end anyways to block fish from getting sucked up the intake tube, so it’ll be hidden.

Incase you’re wondering, what makes the Marineland Emperor and Penguin models different, there’s two things. First, the Emperor is a little more powerful than the Penguin. It circulates more water per hour, so it’s typically used for larger aquariums. And second, the Emperor has a spray bar near the biowheels to spray water on them, ensuring that they keep turning. As a matter of fact, it’s quite common to hear complaints about biowheels getting stuck without the added water flow generated from a spray bar like these, so be careful. If this happens, the beneficial bacteria that has grown wont take long to die off.

Order a Marineland HOB Filter


The general idea of installing an aquarium HOB filter is the same no matter which brand or model/size you go with. Before you go jumping into things, read the manufacturer’s instructions and ensure you have all the parts you’re supposed to have. After that, you want to thoroughly rinse all of the filter media, and anything that is going to come into contact with aquarium water, under cool running water to remove any dust and potential contaminants. Then put all the filter media inside the filter cavity, hang the filter on the edge of your aquarium, and install the intake tube.

Next, you want to make the filter perfectly vertical, otherwise the impeller that causes the suction for the intake tube will rotate at an angle, being very noisy. To ensure it’s verticle, there should be a small plastic piece that you put on the bottom of the filter on the outside, to hold the filter away from the glass wall of the aquarium. Twist it enough so that the filter is straight up and down. At that point, it’s all ready to go, just take a cup and pour aquarium water into the inside of the filter cavity to “prime” it (so it’s not running dry) and plug the sucker in.

If you would prefer a visual representation of how to setup each of the 3 best HOB filters we’ve listed throughout this article, we’ve included some videos below. Just select the name of the filter and the video will appear.




Now it’s worth noting that at this point, even though your aquarium has a functioning filter on it, that doesn’t mean that it’s ready for fish. Your filter will have to “cycle” before you add any animals to the tank. If you aren’t sure what we mean by this, we recommend learning about the Nitrogen Cycle. On the same note, if you are replacing an already-established filter with a new HOB filter, we recommend running both of the filters for a couple weeks before officially removing the “old” filter. This will give the new filter enough time to harbor a gathering of beneficial bacteria so it can support the life of the tank it’s on.

New filters can be a little noisy for the first little while after they are installed. Don’t worry. Just wait until a little slime develops on the inside of the filter and the noise should dissipate. If you go a couple weeks and it’s still not quieting down, you could have a defective filter, and maybe it would be best to contact the store or manufacturer you purchased it from.

Cleaning & Performing Maintenance

Just like installing, the general idea of cleaning and performing maintenance on HOB filters is the same no matter which brand or model you have. First, unplug the filter. You never want to do any sort of tinkering around while the motor is still running. It’s just common sense.

Once it’s powered off, you want to remove the filter media from the filter and dunk it in aquarium water you have just siphoned out of your tank, or dechlorinated water. If you clean it in regular tap water, the chlorine will kill all of the oh-so-valuable beneficial bacteria in your filter media, causing many problems for the life in your tank.

Sponges should be dunked and squeezed until they run clear. The carbon and biological media should just be dunked to remove any debris that may be stuck in them. As long as they are not broken or anything, the sponges and biological media should not be replaced, but carbon media is a different story. Depending on your tank, how much carbon you have, and how often you clean it, it’s effectiveness will deplete over time. Most people say you should replace it every 3 weeks to 3 months to ensure it’s working properly.

If you want to be super thorough with your cleaning, you can also remove the intake tube of your filter and use a bristle brush to remove the build-up on the inside of it. This will keep the filter’s flow running smoothly, without any blockages. You want to be careful, however, it can be a bad thing if you over-clean your filter. If you remove too much beneficial bacteria, you can cause your tank to cycle, putting your fish at risk to toxic water parameters. As such, we never recommend wiping down or cleaning the inside of the filter cavity where all the filter media resides.

We recommend cleaning your filter like this with every water change you do. Doing so will ensure that you remove all the debris and decaying fish poop, uneaten food, and plant matter, so that they don’t increase the concentration of ammonia in your aquarium. You can do it less frequently if you desire, but your water parameters wont be as pristine.

Another thing we recommend to do every couple months or so is cleaning the impeller of your filter. If anything large or stringy gets sucked up the intake tube, it could get caught up in the impeller, causing the filter to be quite loud. As a matter of fact, if your HOB filter is ever abnormally loud, this is probably what happened. Just remove the impeller, and using removed aquarium water or dechlorinated water, rub off all the sludge and build-up on it. Also use a Q-Tip to clean out the compartment where the impeller resides when the filter is running.

After you are done cleaning and performing any maintenance on your HOB filter, put all of the pieces back together and, just like when you first installed it, use a cup to fill up the filter cavity where the media is before plugging it back in. Running it dry can, without a doubt, cause some issues.

Media Customization & Optimization

It’s quite common for many fishkeepers to buy a filter and just run it with the media that the manufacturer intended it to be run with, nothing more. And there is definitely nothing wrong with that. However, it can be a great idea to customize your media to your specific needs and optimize it to its fullest potential.

One of the simplest ways to increase the filtration that your hang on back filter does is by adding a pre-filter sponge to the end of the intake tube. Doing so will increase the number of stages that your water must pass through during its journey through the filtration process. It will stop debris from going into your filter cavity, decreasing the amount of time it takes to clog the sponges. It will provide more surface area for beneficial bacteria to grow. It will even allowing you to potentially reduce the amount of sponge on the inside of your filter, freeing up more space for other types of media.

Cory from Aquarium Co-Op put together a great YouTube video that explains this idea in much more detail, with many more examples. It’s a little on the long side, but if you’ve got the time, it’s a great way to learn a neat trick.