Sump Filter for Freshwater Fish Tank

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There are many types of aquarium filters out there. You have small HOB filters for nano tanks and large canister filters for aquariums of 200 gallons and up.

But what about the in-betweens? Today, we’ll review one of those less-discussed options— the sump filter.

Want to learn more about this filtration system? Can this filter help you create the setup and display of your dreams?

In this article, I’ll cover the sump filter’s pros, cons, and varied applications. Keep reading to find the answer to your sump-related questions.

What Is a Sump Filter?

A sump filter is one of the many types of filtration devices you can use. This one is more discreet than regular internal and hang-on-back filters.

You can easily tuck it away in any aquarium cabinet or stand.

The sump is a tall container, usually separated into multiple chambers where you can put your filtration media.

The sump connects to the main tank through two tubes— a drain pipe and a return pipe. Through these pipes, water leaves the tank, flows through the filter media, and then travels back to the tank.

It’s a pretty simple system with not a lot of components. Besides the container, you’ll also have an overflow box, a return pump, and some tubing to connect the overflow box, the sump, and the pump.

Depending on the size and setup of the sump, you can fit in various types of filter media.

Some sumps are even specially designed to fit a protein skimmer. This makes sumps a viable option for hidden filtration in reef aquariums.

Can You Use a Sump Filter for a Freshwater Tank?

You can fit a protein skimmer in a sump filter. This is great because you can use a sump to maintain your reef tank.

But that’s not the only use of a sump filter. Indeed, this filtration system is also appropriate for freshwater aquariums.

The beauty of a sump filter is that it’s highly customizable. You can add any media you want. The filter chambers are pretty big, so you can keep a ton of biological and chemical media.

You can add a skimmer or leave it out. It’s up to you. This versatility makes the sump filter a good option for most aquarium setups.

Just a heads-up, though, this type of filter is best suited for medium-sized or low-bioload aquariums.

Sump filters can fit a lot of media, but they don’t have a large output because they aren’t very powerful. If you have a heavily-stocked fresh water tank, a sump filter might not be your best choice.

If you still want the neat, hidden-filter look, you should opt for a canister filter instead.

How Does a Sump Filter Work?

You can think of the sump filter as a three-part mechanism. The three parts in this circuit are the outflow box, the sump itself, and the return pump. These elements form a loop, keeping constant water movement and filtration.

Here’s how it works—

  • The sump holds extra water that would otherwise overfill the aquarium. The water needs to keep moving so that the aquarium doesn’t flood.
  • The return pump sets the water into motion. The pump takes the water from the sump and pushes it into the tank through the return pipe.
  • As the water returns to the tank, the total volume increases. The water level begins to rise until it sets off the outflow box.
  • The outflow box siphons the extra water and lets it drain down a tube and back into the sump. This siphoning keeps the water from rising to the point of flooding the tank.
  • Once inside the sump, the water travels through the media-filled chambers. The water is filtered and ready to go back into the tank.

How To Setup a Sump Filter?

Setting up a sump correctly is crucial to avoid technical issues down the line. So, let’s go over the process step by step.

Just a heads-up first— I’m not going to go into how to make a DIY sump, which is a common practice in the aquarium hobby.

Many people choose to make their own sump to cut costs, but that’s beyond the scope of this article.

Instead, let’s look at how to set up a prefab sump filter:

Step 1: You first need to create a drain for your aquarium. That’s where the water will leave the tank to flow down into the sump.

You can do so in two ways, depending on the type of drain box that comes with your sump filter.

If you have a hang-on-back overflow box, you just have to hang the drain system on either the left or the right side of your tank. It’s best to place the drain in the opposite direction of the return pump.

So, if your pump goes on the right side, the overflow box should hang on the left side.

Avoid putting the box in the center, as this can minimize the siphoning action of the drain.

If you have an in-tank drain, you’ll have to drill a hole in the aquarium wall. You should use the same positioning rule as before— the drain goes on the wall opposite the return pump.

Step 2: If you’re buying your sump components separately, it’s time to prepare the plumbing.

The overflow box needs two standpipes— one Durso standpipe for the drain and one pipe with a flare return nozzle for the return pump.

You’ll also need four bulkheads to connect these standpipes to some flexible or PVC tubing, which then goes into the sump.

Use one bulkhead to connect the drain tube to a filter sock. The other bulkhead is for connecting the return pipe to the pump.

Step 3: Get the sump components ready. These need to go into the correct order if you want efficient water filtration.

Typically, the sump separates into three or four different chambers. Each one houses a different type of media.

The first thing that goes into the sump is the filter sock. This connects directly to the drain tube.

The filter sock offers mechanical filtration, similar to a pre-filter sponge. The next chamber is for biological filtration. You can include gravel, ceramic rings, and ammonia rocks in this section.

After the biological filtration, the next chamber is best suited for chemical filtration. That’s where you’ll put the activated carbon pellets. Some sumps have an additional narrow room for a bubble trap.

The last section of the sump should house the return pump. After you got everything in order, hook the return pump to the return tube, and your filter is ready to run.

Benefits Of an Aquarium Sump Filter

There are multiple filters to choose from, depending on your needs and preferences. Each filter has pros and cons, so it’s best to get a clear picture before buying one.

Let’s discuss the benefits of a sump filter, so you can decide whether it’s the right choice for you:

Sump filters are compact and easy to hide.

A sump filter is perhaps the best option if you want a clutter-free display. The filter itself sits hidden in the aquarium cabinet.

But the layout and the mechanism of the sump also let you tuck away other distracting elements. Water heaters, protein skimmers, and air pumps can fit neatly into the filtration container.

They’re very versatile.

The filtration container is spacious and well-designed. There are multiple chambers of varying widths. Like in any other filter, you can fit filter floss, bio media, and carbon pellets.

You can also add a protein skimmer and calcium reactor into or beside the container. The versatility allows you to customize your filter according to any setup, whether you have a freshwater, softwater, marine, or hard water aquarium.

They’re very quiet.

Sump filters don’t produce a lot of noise, to begin with. But it gets even better because this setup allows you to hide all the buzzing equipment in the aquarium furniture.

The cabinet will do a lot to muffle the background noise created by the pump, heater, and protein skimmer.

They increase the water and oxygen volumes in the tank.

This is a unique perk of sump filters. This filtration system relies on overflow to maintain constant water movement. This means that the sump holds extra water that would overfill the tank otherwise.

The additional volume dilutes the tank water, making it more stable against nitrates, pH, temperature, and salinity fluctuations. The constant movement through the sump chambers also helps dissolve additional oxygen into the water.

They’re affordable and cost-effective.

Half of the work done by the sump filter is thanks to the free movement of water. You only require energy to power the return pump.

Besides, this filtration system is among the most simple and affordable external filters. Canister filters deserve the hype for being clutter-free external filters.

But they can also get costly and come with considerable operational costs. Sump filters can achieve similar results with a fraction of the costs.

Drawbacks Of an Aquarium Sump Filter

Of course, no objective analysis would be complete without considering the drawbacks of a product.

Even the best filter on paper is not perfect. And as good as they are, sump filters still have a few disadvantages worth discussing.

Here are the main downsides to be aware of:

Sump filters aren’t very user-friendly.

With some filters, it’s as easy as adding the tubbing, connecting the filter to the tank, and running the whole thing.

Even bulky canister filters come with the media pre-packaged. The most common filtration systems now come with “smart” pumps, making for a quick and easy startup.

Well, sump filters aren’t as straightforward. The overflow box, the tubing, and all the filter media need to be installed in the right place.

Otherwise, you risk technical issues. Priming the pump is also a common pitfall and might be more difficult than with other filters.

Proper placement of the overflow box takes some trial and error.

The overflow box is the most troublesome part of the sump filter installation. It’s so tricky and annoying that it deserves a special place on this list.

There are a variety of overflow sizes and shapes, which doesn’t make the job more straightforward. Most importantly, different overflows have different installation methods.

Some are simpler, hang-on-back models, while others would require you to drill your aquarium.

Obviously, drilling a hole into your tank is a project you can only attempt once. Definitely pay close attention when purchasing the sump filter equipment.

They aren’t very powerful.

Sump filters are excellent for keeping the water clean. If they can keep up with the demand, that is.

As I’ve already mentioned, sump filters pale in comparison with canisters. The power you’ll get from the return pump is not enough to produce a high output.

This makes sumps a poor choice for very large aquariums (think 100 gallons and up).

They’re not as durable as other options.

Sump filters require regular maintenance and media replacements. The motor pump on such filters is also more susceptible to wear and tear, which makes these systems less durable.

Finally, the sump itself is made from fragile materials, typically glass. This makes the container vulnerable to shock damage. Even small cracks could require you to replace the sump in case of a minor accident.

Technical issues can lead to flooding.

Sump filters increase the volume of water circulating through your tank. When everything works well, the overflow box siphons excess water out of the tank, through the sump filter media, and back into the tank through the return pump.

If the outflow or return pump malfunctions, the loop is broken. This means all the excess water in the sump will get back into the tank.

Next thing you know— all the overflowing water is now all over the furniture and the floor.

How To Maintain a Sump Filter?

Sump filters need regular maintenance to function at full parameters. Luckily, maintaining a sump is relatively easy once you build a regular routine.

We can split the sump maintenance duties into two categories:

Weekly chores: This process is no different from maintaining a regular aquarium filter. You’ll need to clean the filter socks once a week. Really, that’s it.

Just clean up any gunk that has been collected on the filter sock. Otherwise, the debris could prevent proper water drainage into the sump.

If you use a protein skimmer, now’s also a good time to empty the protein skimmer cups to avoid overflow issues.

Monthly chores: You should thoroughly clean your sump once a month. This includes cleaning the sump walls, rinsing sponges, cleaning biological filter media, and replacing your carbon pellets.

You should also inspect any equipment in the sump once a month. Check the return pump, protein skimmer, heater, or media reactors for any possible issues.

Sump Filter Vs. Canister Filter – Which Is Best?

Both sump and canister filters have similar upsides. These filters are neat, low-noise, and create a clutter-free display.

Most importantly, both filters keep the water crystal clear. So, which one should you choose?

Well, this will depend on your setup and preferences. No filter is perfect, so you have to weigh the pros and cons of both to find the perfect one for you.

Here’s a quick rundown of both filters:

  Filter type
Sump Filter Canister Filter
Pros Can hide more aquarium equipment (heaters, protein skimmers, etc.)

Creates a larger water volume.

Easy maintenance.

Can fit in most aquarium stands.

Endless customization options.

It’s cheaper than a canister filter.

Easy to install.

Very high output.

Suitable for medium to very large tanks.

Very durable.

Less noisy than a sump filter.

Some offer superior mechanical filtration.

Cons Has a lower output than a canister filter.

Not suitable for very large aquariums.

Setup can be tricky.

Not as durable as other filters.

Prone to leaks and flooding.

Very pricy.

Most filters are very tall, not fitting in small aquarium cabinets.

Lower media capacity than a sump.

Can’t hide other aquarium equipment.


Overall, a sump filter can do anything a canister filter can do. If you have a medium-sized aquarium and don’t need a huge output, the sump is an elegant and affordable choice.

It hides aquarium equipment very well, and the extra water volume makes aquarium management a breeze.


The sump filter is one of the best choices for medium-sized marine or freshwater aquariums. This filter has insane media capacity and can even house other unsightly aquarium equipment like heaters, skimmers, and reactors.

It’s the perfect alternative to the bulky and overpriced canister filters on the market.

Setting up a sump filter takes some trial and error. But once you’re done, aquarium and filter maintenance becomes easier than ever.

If you’re looking for a discreet, versatile, efficient, and cost-effective filter to transform your aquarium display, look no further than the humble sump.

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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