Whatever Happened to the Box/Corner Filter?

In the beginning of home aquariums, box filters (also known as corner filters) were the only means of convenient filtration for aquarists. But in the past decades, new gadgets have been developed in order to provide other means of filtration, such as other internal filters like the sponge filter, undergravel filter, and the now ever-so-popular external filters like the power (waterfall, HOB) filter.

Each type of filter has its own unique design of filtering out pollutants in the water. No type of filter is perfect, however, as there are always some drawbacks to the kind you choose. But why is the box filter, the oldest means of aquarium filtration, nearly extinct? Walk into any chain store’s aquarium section and you’ll find no box filters on the shelf. In fact, search for them online and you’ll find they are almost always on sale, as if stores can’t get rid of them.

Only the local aquarium store may have a few box filters on the shelf, but most likely you’ll have to buy yours online after some heavy searching.

So what’s the deal? I will go over what the box filter is, its pros and cons, and my own theory as to why it is disappearing. I will contrast the box filter with the power filter, because it is the most popular filter and I have no experience with the other types.


The Box Filter

I prefer the name “box filter” rather than corner filter, because I tend to think of corner filters as the triangular ones designed to be in a corner, while there are round and square filters that are meant to be placed anywhere. So it’s like all corner filters are box filters, but not all box filters are corner filters, even though all of them are almost always placed in a corner anyway. It’s just my preference of name. And the filter, no matter what shape, is like a box, containing its entire media inside.

The box filter is air-powered and one of the simplest filters in design and materials. It is a clear plastic box (or whatever shape) with slits on its side and/or top where the intake takes place.

Charcoal is the most common filter media, and it is compacted by aquarium filter floss (cotton-like) placed on top and/or bottom, which serves as mechanical filtration. In order to make the filter work, it needs an air pump motor and a clear tube that is meant for air stones; the air rises up through the filter, while water is sucked into the slits through the mechanical and chemical media.

It is very simple when you see it in action.

Why I Love the Box Filter

Cheap in Every Way

The filter itself can be a few dollars to $10; the higher price range is meant to filter larger tanks. Once you buy the filter, the pump, and the tubing, all you will ever need to buy is the floss and what other media you use. Active carbon and floss are often sold in bulk, so you can buy a year’s worth of floss or more for just $8. Carbon or other media are often pricier, but once you buy it you are set for a long time.

The power filter by itself is more expensive because a motor is a part of it; you have everything you need from the get-go, but this also means more money. Instead of buying floss and other media separately and in bulk, power filters use cartridges that combine the floss and carbon into one, with the addition of plastic boarders that keep everything in place. They also have different sizes for different size filters, so you are very limited on your choices. And because they come with plastic sides, sown-like pockets of floss, and carbon conveniently in place, it is more expensive.

In the end, a power filter will cost you at least five times the amount of a box filter in media.

Perfect for Slow Moving Animals

A power filter creates a current underwater, so if you have slow moving fish or small, weak critters, a power filter can make life for your animals stressful. Of course the bigger the tank, the less likely they’ll have to put up with the current. They do make adjustable power filters to control the strength of the water flow, but these are a lot more expensive than the preset ones.

The box filter only disrupts the surface, and even this current isn’t that strong. If a box filter is placed in a small aquarium, and surface turbulence is an issue, merely place floating or tall décor in the path of the ripples so your air-breathing animals have some calm water to come up to. Remember that the current on top does contribute to aerating the water, so don’t cut off most of the turbulence.


It’s no wonder so many people say box filters are perfect for fry and breeding tanks. There’s no current underwater so the smallest fry can swim freely, and the filter intake isn’t as strong as a power filter. There are plenty of horror stories of little fish getting sucked into the power filter’s intake, but box filters’ strength isn’t as strong. While the filter does have slits big enough for the tiniest fry or African dwarf frog legs to get into, combined with the low intake, the filter floss behind the slits prevent animals from getting past. You may find your shrimp pulling out some of the floss through the slits, but they will stop once they realize there’s no food in the floss.


Unless the manufacturer uses the thinnest layer of plastic possible, the box filter lasts. I have one that’s been in use for 20 years, and besides a chipped off piece on the bubbler tube (where bubbles come out), it’s held up.

Because power filters are much more complex than the box filter with moving parts and a connected motor, if it stops working then odds are you’ll have to buy a new one. If the motor dies, you can’t just replace that part. If your aquarium has hard water and the hardness accumulates inside it, it will eventually clog and there may not be a way to get rid of the built up deposits deep inside.

Easy to Clean

As mentioned above, the power filter can become ineffective in time, which is why it needs to be regularly cleaned. I clean my box filters maybe once a year, and it’s easy because you have access to everything. The only part that requires a pipe brush is the air intake and bubbler tube, but because of the tube sizes, it would take years for accumulation to build up to the point of slowing down the air flow, if at all. It’s a quick simple clean, and convenient to do so when performing a media change when the box filter has to come out of the aquarium.

Can be Used during Power Outages

This goes for all air powered filters. Battery-operated motors are typically used for air stones while transporting fish, but it can also pump air into your box filter during an emergency when you have no electricity, so your tank will continue filtering and your fish won't be jeopardized. I think everyone with an aquarium should at least have one battery-operated motor and an air driven filter as a safety measure. Only a generator will keep other filters working during a power outage.

And out of the three types of air filters, the box filter is the best option in case of an emergency, because you can take your filter's biologically established media and place them in the box filter (in order to keep the nitrogen cycle going--the main point of having a filter). Can't do that with a sponge filter and would be challenging to do so with an undergravel one.

Variety in Media Options

As I've already established, the box filter differs from the other air driven types due to its unique design. While sponge filters only have sponge material as filter media, and undergravel filters use, well, gravel, the box filter is the best choice if there are particular media you want to use.

There's (mechanical) filter floss, sponges, (chemical) activated carbon, zeolite, phosphate absorbents, peat, crushed coral, (biological) gravel, ceramic rings, lava rocks: whatever you want, you have the option. Sponge filters and undergravel filters can still provide excellent biological filtration (as well as mechanical for sponge), but if looking for an air powered filter where you can have all three methods of filtration (mechanical, chemical, and biological), the box filter is it.

Filter floss, frog moss (pH experiment), ceramic rings, and gravel.
Filter floss, frog moss (pH experiment), ceramic rings, and gravel.

Criticisms of the Box Filter


I have read that some people say the box filter is ineffective. The power filter is stronger and filters more water per hour than the box filter.

This is true; power filters are stronger. But to say the box filter is ineffective is false. I’ve used box filters all my life and they do a great job sustaining my tanks.

Like any filter, not all sizes are meant for the same size tank. There are box filters for 10 gallons and then some for 40 gallons. The average, old fashion box filter (made by Lustar for example) is best suited for 5-25 gallon tanks, so it would only be ineffective if placed in a much larger tank. Or, if placed in a tank with a high bio load (amount of fish waste).

Power filters can (depending on its size and the tank size) manage higher bio loads, while box filters are better suited for low to medium bio loads. So it's possible that a box filter may not be enough in a 20 gallon if it's housing goldfish or large schools of fish - anything that produces a high amount of waste.

If wanting to use box filters for a tank larger than 25 gallons or with a high bio load, I'd suggest using two box filters in opposite corners. Not only does this ensure you're getting enough surface agitation and filtration in longer tanks, but it makes partial media changes safer, as you will always have one filter with all of its beneficial bacteria.


I’ve read some people think the box filter is ugly and ruins the look of the aquarium. I guess that’s just a matter of opinion. I don’t think they’re beautiful, but ugly? A heater isn’t attractive, but it serves its purpose and I don’t mind the view of it either.

Personally, I think this is a petty reason not to use box filters. I understand that if you’re going for a natural-looking atmosphere, the filter does ruin the illusion. If this is truly a concern, merely place a fake plant in front of it and it’s hardly noticeable. This is why I prefer (and miss) Lustar’s green filters, because the greenish tone of the plastic blends in with the background better. Recent box filters like Lee’s are just clear, so the floss remains white and sticks out a little bit (before it eventually turns brown or gray). But that won’t stop me from buying one if one of my filters did break, somehow.

Lee's filter with air stone, sitting on shelf of LFS.
Lee's filter with air stone, sitting on shelf of LFS.


Some people complain about the sound of the box filter, when really they are referring to the motor. Some motors, like older ones, are loud due to the vibration. I'd suggest finding a quieter motor, as this would be the same problem with a sponge filter or undergravel filter.

The traditional box filter with a bubbler tube does make a “blublublub” sound, but unless it is right next to you, it’s just white noise in the background. Air stones are a lot nosier, and some current box filters are designed to have an air stone inside of them. Still, it’s a light sound that one gets used to pretty fast.

If there is concern for the animals, they also appear to get used to the light vibration. If they are used to no filtration, it might be jarring to them at first, but after a few hours they should return to normal behavior. All my fish and critters act calm and normal, but some animals might be sensitive to vibrations, so it just depends on the animal.

A power filter can be noisy if the water’s surface is far away, making a trickling sound that I’d imagine humans and animals can get used to as well.

Takes Up Too Much Room

Now this is a legitimate concern. Box filters are great for filtering small aquariums, but if the tanks are too small, space can be an issue.

Box filters come in different sizes. The smallest are about a pint while the larger ones can be almost a quart (1/4 gallon). So let’s say you have the larger one. If you place it in a 5.5 gallon tank, it reduces the space to 5.25 gallons. To me, this isn’t a big deal, but it could be for someone else, depending on what they are putting in there. For a 10 gallon, the space left would be 9.75 gallons. Again, seems minor, but more space is always better. The power filter doesn’t take up any room because it hangs on the back of the tank.

Of course, people forget that while a box filter does take up a little bit of space, it can serve another function; a hiding place. My bettas, ghost shrimp, and African Dwarf frogs love hiding behind and underneath my box filter. To them, it’s just another place to explore, or hang out to feel secure. This bonus can make up for taking up half or a full quart of space, so this is something to consider.

Anything less than five gallons is a real issue. Ghost shrimp and snails won’t mind, but fish (including a betta) need as much space as they can get when in a tank that small. It’s hard to filter a tank smaller than five gallons, and I’d suggest either getting a larger tank or performing water changes as a means to keep nitrates down. The latter is a lot more work though. A lot of live plants could help make changes less frequent.

Hate the slanted top but like the permanent stationary piece. If you have no substrate, some smooth rocks will do.
Hate the slanted top but like the permanent stationary piece. If you have no substrate, some smooth rocks will do.

Difficult to Station

This should be blamed on the company's design rather than the filter itself. Box filters have come in all shapes and sizes over the years, but some design aspects are questionable. Since these filters are air-driven, they tend to float unless they are anchored. Almost all box filters come with a stationary piece that is meant to be bunkered by gravel. The older models’ pieces are detachable, and why, I do not know. So you can lose them and not be able to keep your filter in place? Later ones have the stationary as a permanent part of the filter (or at least tougher to detach), although this puts people who don’t use substrate at a disadvantage.

If you lost the stationary piece and the filter has a flat top, merely place a rock on top of it and it will hold whether you have gravel or not. Unfortunately some box filter designs have slanted tops instead. Reminds me of my high school lockers with the same slant; just WHY? These two design flaws can be frustrating, but they can be dealt with.

Using suction cups meant to anchor air stones on the wall can help tremendously; just attach the suction cup to the tube above the filter (by a few inches) and it will at least stay down.

You could always just place rocks or gravel inside of the filter. In fact, one of my box filters consist only of gravel and floss (makes great biological filtration!)

Messy Maintenance

I understand this criticism all too well. Probably the biggest reason why people prefer power filters over box filters is the quick, convenient way to change out the filter.

With a power filter, one just needs to slide out the cartridge and slide in a new one. Let’s contrast this with the box filter’s media change.

The box filter needs to be unplugged, the tube detached, and then the filter taken out of the water. You’ll need a bucket or bowl to immediately place the wet filter in, as some box filters leak a lot. Once at the sink, take off the lid and remove the floss and whatever media you have.

If dealing with active carbon, especially wet carbon, it tends to cling together and makes it challenging to replace in a box filter. Washing it out is simple, but then you must rinse out new carbon before placing it in the filter, and that is a messy job. While you’re trying to remove the wet carbon into the filter from a strainer, you’re also trying to avoid getting any down the bubbler. Once you’ve put the floss back in, seal everything in with the lid and put the filter back to work, it is not uncommon for some carbon to shoot out of the bubbler, creating a little volcanic simulation. As long as your animals don’t eat the carbon, it won’t hurt them. I’ve seen my betta snatch a descending charcoal piece and immediately spat it out. If consumption is a concern, take a washed turkey baster and suck up any remaining charcoal in the water. The spewing of charcoal shouldn’t last very long.

See the difference in changes? One’s easy and the other is a bit of work. Here are my suggestions for making box filter changes easier.

Let the Box Filter Serve as the Strainer

Cut out the middleman and just pour the dry carbon into the filter. Then fill it up with water and let the water rinse it clean. Even if your filter doesn't leak at the bottom, it will leak when tilting it so water runs through the slits. Use that to your advantage and let it get rid of the powdered carbon. Once the water pouring out from the filter is clear, you’re done. Of course, you may still have some loose carbon that will be taken up through the bubbler, but it should be minimal.

Filter Bags

This is an even easier way to deal with wet carbon. Filter bags can be purchased at local aquarium stores, and maybe some chain stores. They are bags that allow water flow and are perfect for placing charcoal in. You can rinse the carbon in the bag, have it washed out, and place it in the filter with no complications. You may not be able to get rid of all the wet carbon out of the bag so easily, but it’s actually healthy to keep some old carbon, as it contains good bacteria that break down ammonia and nitrites. The bags are only a few dollars, but you could use a cut pantyhose footing for the same effect for free.

Just Don’t Use Carbon

Is chemical filtration really necessary in an established tank? A lot of aquarists say once you have a stable setup, there’s no need for carbon, unless there is medication that needs to be removed from the water as soon as possible. In fact, carbon can soak up good nutrients that live plants benefit from, as well as medication that your sick animals need. Also by not using carbon, you only need to replace media when the floss starts to deteriorate, and even then you don’t want to get rid of it all because of the good bacteria inside.

So carbon may just be an unnecessary nuisance from the start, and replacing it with gravel or ceramic rings will mean not having to change your filter at all, although you will want to rinse the media off once in a while as debris will build up over time. Of course, this also means even less money for your filtration, as carbon isn’t cheap and needs constant replacing.

There is a disadvantage to performing the quick cartridge media change for power filters; you are taking away your beneficial bacteria by fully replacing your media. This removal of bacteria (in the most important place for the bacteria to be) can overwhelm your nitrogen cycle, resulting in a mini cycle. This will cause ammonia and nitrite to develop in your tank, and this toxic presence could last a day or a week, depending on many factors. This is why partial media changes (or simply rinsing used media in aquarium or dechlorinated water) is safe and encouraged in aquarium keeping. So instead of changing out cartridges, simply rinse the floss encasement with aquarium water (as chlorine in tap water kills bacteria) and replace the carbon if you wish to continue chemical filtration.

Of course this is more work, almost as much as partially removing and safely rinsing media in corner filters.

Convenience Outweighs Everything

Despite my points and rebuttals, it seems people just want things to be easy. Even if you use a filter bag or no carbon at all, five minutes is a century compared to five seconds of media maintenance. And the sad fact is a lot of people who buy fish and aquarium setups don’t really know that much about good aquarium keeping. Someone will buy an animal before doing any research and place them in a small tank with whatever filter is being sold on the shelf, and they just fill it up with water and drop it in. They want the easiest setup. Actually, all setup kits I have seen have preset power filters as part of the package, and people will assume that this is the best filter, even for a five gallon.

I believe this is why the power filter is so popular while others are being pulled off the shelf, because it’s easier. It’s not that the power filter isn’t a good filtration system. If I had a 55 gallon tank, I’d either choose HOB's or a canister filter for it; power filters are definitely needed for certain aquariums, especially housing river-dwelling fish that enjoy currents.

What bothers me is that most stores don’t give you a choice. It’s almost always a power filter, and maybe a canister filter. Once in a great while I’ll see sponge filters.

But the box filter, the cheapest option of all, is the rarest and I think it’s a shame that such a cheap, excellent filter is called “old school” or “old fashion.” One person I know referred to it as “out of style.” Really? Aquarium filters are equivalent to our phones now?

I think another reason box filters are a low demand is because they last so long. Once you buy one, the only reason to buy another is if you want to start up a second tank. That or the filter was thrown at a wall. Meanwhile with power filters, companies are making money off the fact that you need their cartridges to use on their filters.

If you’re happy with your filter, and more importantly your animals are too, then stick with what you know. For those looking for a cheap, safe filter for slow moving fish like bettas, angle fish, and gouramis, or other animals like aquatic frogs and axolotls, then consider the box filter. Good luck finding one.

* sell some box filters, where I got the large round green Lustar box filter. It's huge! The rest in the pictures were passed down to me.

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Comments 9 comments

psycheskinner profile image

psycheskinner 3 years ago

Very good summary. I use different types on different tanks. Box, undergravel and HOB.

mariekbloch profile image

mariekbloch 3 years ago Author

Are you kidding me? I just published this like 5 minutes ago. Lol. You're a fast reader. Good to hear you use different kinds. Thanks for commenting.

Terri G. 3 years ago

I love my box filters! I bought a lot of 12 new in box for $7 on Aquabid last year. While the noise from pump and filter does take getting used to, especially in the bedroom, I lose far less fry to the box filters. I do use some power filters on larger tanks, but overall prefer the boxes.

Lawrence K 19 months ago

I fullishly gave away my box filters a couple years ago when I wasn't running any aquariums. Now I can't find find any locally.

I have used them temporarily with a power head to quickly clear the water after disturbing the tank.

Tom 19 months ago

you forgot one little morsel that favors our fogotten box filter. when the power goes out, they don't need to be primed like many hob filters do. they will start right back up on their own. hob's often have to be primed with water to get going again. plus, the bacteria is much less likely to die since they are inside the tank, not in the tiny amount of water in an hob filter. without O2, they will die off. ((::

i started my corner box fitter up recently. it has sat for 40 years unsed. i did have to buy another air pump for a whopping $7.50!

Jay Kooken 19 months ago

Great essay. I agree, completely. I left the hobby in 1990 and returned in 2002. The missing box filter and the missing independent Mom and Pop aquarium shop, have left me with a frown. There are the hand full of shops that you may walk in that have that familiar and comforting sound if the compresor in the back room and the bubbles as you walk the isles, but they are fewer and fewer. I am planning a fish room and there will be a central air compresor with box filters and sponge filters.

Retro 6 months ago

I recently bought an old, "vintage" aluminum frame 10 gallon aquarium and I will be adding a box filter to it. My local fish store still sells them for 9 dollars! I've also found a little aquarium ornament from the 50's (made in japan) on ebay to complete my kitsch tank. My platy fry are going to love their retro home.

Lisa 5 months ago

A well written article that still answers questions today. Wish I'd held onto my old box filters... Gonna try and locate one for my fry tank. :-)

Barbara 3 months ago

I just cleaned out my 10 gallon tank and broke the valve on my old box filter. Was glad to be able to find another box filter on line. So I went ahead and ordered one. Knew I would never be able to find one in my pet store. I do want to check up on the battery pumps in case our electricity goes out. Loved this article very informative.


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