Build Your Own Custom Aquarium Filter Sump

There are a lot of aquarium setups that will do better with a custom sump filtration system. Almost any saltwater tank should have one. Even if it is just a 10 gallon sump on a 20 gallon tank it can make all the difference in how well your tank runs long term and how easy it is to keep it going that way.

The general benefits of a sump include increased total water volume, a place to hide almost all equipment (heaters, protein skimmers, all filtration, etc.), a safe place to add supplements (many additives in a reef tank are best well mixed before going in to the main tank), and even a good place to refill during water changes or add top-off water for a saltwater tank.

build a freshwater sumpbest fish tank sump designhow to build a reef sumpfreshwater aquarium sump design

In freshwater there are some great options for filtration on smaller tanks but once you get to a certain point a sump may end up being the best option. At about 75 gallons it becomes better to use a canister or sump instead of HOBs. This can vary with your experience and preference. If you love a great, big canister and will actually keep up on the maintenance then you will be better off going with a canister like the Fluval FX6. But if you are like the majority of canister filter users who do not clean the canister every month then you may want to consider going with a properly designed sump. They can be easier to maintain. Instead of dragging an entire canister full of water to the sink, tub, driveway, or wherever your significant other has limited you to, you just pull out the foam blocks, the filter sock, the bag of carbon, or whatever needs cleaning. You can swap media out in seconds with little to no mess.

That being said, you will find an endless amount of information online about what the best design is and what you need, what you don’t need, etc. I have seen a ton of designs and many are much more complicated then they need to be. Many are very redundant with multiple stages of mechanical media, repetitive stages, and more.

Over the years I have seen and worked on many sumps, and done a lot of research to come to my current designs. These designs fit the needs of saltwater and freshwater specifically. They meet all the needs of the systems they are designed for. They provide flexibility for you to use any return pump you want, any protein skimmer you want, maximize the refugium space or filter media space, and keep things as easy as possible for you to maintain.

The saltwater design maximizes the use of natural filtration, the refugium. This is where good macroalgae grows. By doing so it removes nutrients from the water column thus minimizing the amount of nutrients left available for bad algae to grow in the display tank. The sump design also allows you to use almost any skimmer you want. In-sump skimmers are larger and much more effective than skimmers designed to just hang on the back of the tank. The fact that they are in the sump also means that if they ever overflow for any reason they overflow into the sump, not down the back of your tank, on the wall and floor, etc. The saltwater design also allows you to easily add an automatic top-off system, media reactors, and many other things you may decide to add to your system. You can even add a hang-on filter sock holder.

Why Not Use A Manufactured Sump?

There are a lot of manufactured sumps out there, and many are much better than others. But the problem with any of them is that they are designed for one specific use and do not have any flexibility. If you want to use a specific skimmer you may only have one or two options of manufactured sumps that are large enough to fit it, and they may not fit in your stand. Many also have features that are unnecessary, so in order to get everything you do want you also have to pay for the features you either aren’t worried about or flat out don’t want. One manufactured design I saw that was one of the better ones and quite popular actually has the skimmer right next to the return pump. This means that if any bubbles make it out of the skimmer they will be pulled in by the pump and pushed into the display which can look horrible and drive you crazy. So even these professionally designed sumps don’t always seem to be designed well for practical uses. You may find exactly what you want and prefer to go with a manufactured sump, but in my experience you end up paying a lot more for no flexibility.

Making your own sump may sound daunting but if you take the time to finalize a great design the actual assembly is not bad at all. The supplies needed to actually assemble the sump are the tank, glass baffles, caulking gun, silicone, tape measure or ruler, permanent marker, small level, and a couple 1/2″ PVC elbows to use as a spacer for any baffles that are supposed to be off the bottom. The PVC elbows can be placed on the bottom of the tank and will perfectly space any baffles that need to be 1″ off of the bottom (the outer diameter of the elbows is 1″). I also use a product called Pro Caulk, which you may have seen on TV, which just allows you to give a nice finish to the silicone, but that is up to you.

Saltwater Design Specifics:

Smoked Baffles: Smoked baffles prevent the light on the refugium from growing algae throughout the entire sump, which can be a pain if not almost impossible to keep clean. Smoked glass does cost a little more than clear, but since you only have to make the sump once it is more than worth it for all the work it will save you. All baffles in a sump with a refugium should be smoked to help prevent as much algae as possible. The smoked glass should be the darkest that the glass shop has available.

Minimal Baffles: My standard design uses only four baffles. The first baffle keeps the water level around the protein skimmer stable. This is very important since most skimmers are a little tricky when it comes to getting them adjusted properly and any change in water level can completely undo your fine tuning. The second baffle drives water down, which helps minimize any bubbles coming from the skimmer and input to the sump (drain from the tank). The third baffle drives water up again (again, helping to fight bubbles) and helps contain the refugium. The last baffle keeps the macroalgae in the refugium from getting to the pump section which helps prevent the pumps from clogging.

Maximum Refugium Space: By knowing which return pump and protein skimmer you will be using you can keep those sections as small as possible which leaves the maximum amount of space possible left for the refugium. These means there is that much more space for the refugium to be effective while still providing all the needed space for the skimmer and other equipment.

Mesh Baffle Wall: The last baffle is designed to keep macroalgae and fish out of the pump section. It consists of eggcrate on both sides of a glass baffle. The glass baffle is only six inches high and the eggcrate extends to the estimated water line. Between the two pieces of eggcrate is a sheet of needlepoint canvas (plastic mesh) that extends above the water line. The eggcrate is siliconed to the glass baffle and holds the needlepoint canvas in place. The needlepoint canvas is not attached in any way, it is just held in place by the eggcrate. This creates the perfect wall to keep macroalgae and fish out of the pump section with minimal maintenance. The needlepoint canvas can be black or white. White will show how dirty it is better so you will know when you need to clean it. Black will help keep even more light out of the pump section (preventing algae). This one feature can save you a lot of hassle by keeping stuff out of the pump section, including valuable fish that inevitably make their way in to the sump.

This feature is one of the best things about this design. I have gotten emails calling it “genius” because of the fish it has saved for people. I have also talked to people whose sumps do not have this or an equivalent feature and lost fish that were pulled in to the pump.

Easy Maintenance: The needlepoint mesh used with the last baffle to keep the macroalgae out of the pumps is very easy to remove and keep cleaned.

Glass Lid: By using a clear glass lid you can dramatically cut down on the noise, splash and salt creep, evaporation, and keep electrical equipment out of the sump. This is the perfect place to set your refugium light and be sure it won’t end up submerged.

Options for Custom Reef Sumps:
-In-sump reservoir for automatic top off system.
-Slow flow refugium.

There are a few options you may decide to easily add to the standard saltwater sumps. My design allows you to easily add:
-Automatic Top Off System
-Media Reactors
-Filter Sock Holder: may require some extra space in the skimmer section. Eshopps and CPR Aquatics both make a hang-on filter sock holder. There are also many designs available online to make your own filter sock holder, usually using eggcrate.

Standard Saltwater Reef Sump Design:

build a custom saltwater reef refugium sump filter

Freshwater Design Specifics:

First Baffle: The first Baffle leaves a space where the water comes in because if you don’t do this it can make it very difficult to get the foam and other media in and out with the PVC from the drain coming down and getting in the way. Leave this section if at all possible.

Foam Block/Mechanical Media Section: Between the first and second baffles is a foam block that very effectively removes physical debris, extra food, etc. It easily slips in and out and can be used over and over. Since all the water going through the sump passes through the foam block, it is extremely effective. I prefer Eshopps Square Foam because they are the right thickness, pore size, etc. You will want to decide on the exact foam block to use before finalizing your sump’s design so that the baffles are the right width apart, otherwise the foam block won’t fill the space between the baffles snugly and will be ineffective. Unless it is a small sump on a tank with a low bioload, position the foam block sideways, not upright. This gives more surface area for the top of the foam so it doesn’t clog up as quickly. You can also double stack the foam blocks.

You can use filter pads if you prefer, but I prefer the foam blocks because they can be used over and over again.

Chemical Media – Below the foam block is the ideal place to put any chemical media you may be using. This may be carbon, crushed coral, Purigen, GFO, Poly-Filter, or anything else For more information on the media selection, please read the Filter Media Guide.

The bottom of the media stack should be held up by eggcrate supported by PVC couplers. If you use these couplers to hold up the baffles that need to be off the bottom when installing them, everything will line up perfectly.

Filling the space below the second baffle should be eggcrate with plastic mesh zip tied to it. This can be done by siliconing the eggcrate to the glass or making a small assembly made of the eggcrate for the bottom of the media stack, the supporting PVC coupler, and the eggcrate/plastic mesh against the K2 section.

K2 Media Section: This is a revolutionary, self-cleaning filtration method that utilizes a floating plastic media called K2. It has been used in waste management and on fish farms for over 10 years, but has only recently been brought to the aquarium hobby. This section is partially filled with the specially designed K2 media which is kept tumbling and strongly aerated by strong air stones. This tumbling action helps break down waste and keeps the media itself clean. The media then becomes an ideal site for beneficial bacteria because of the aeration and water flow.

K2 media is small enough to fit through the eggcrate. This means that you need to use needlepoint canvas between the K2 and the pump section.

The K2 should fill approximately 60% of this space. Since K2 is sold on eBay and other sources by the volume, it makes it very easy to calculate how much you need to buy. Just determine the volume of the K2 section (accounting for the actual water level line, not all the way to the trim of the tank) and multiply by 0.6, and that will be how much K2 you need to buy.

Air stones (standard 1″ air stones) are better than bubble wands because they concentrate the flow of bubbles, which greatly increases the flow they create. The air stones can be kept in place with suction cups on the bottom glass of the sump, or by attaching them to small stones with zip ties. I usually run the air line to a tee, then use just enough air line to connect two 1″ air stones. So each spot in the sump with air actually has two air stones.

Last Baffle Wall: The last baffle looks a little complicated, but is actually a very simple and effective design. The glass baffle itself is nice and low at only 6″ tall so that the pump won’t run out of water. This means the water level in the whole sump varies instead of just the very last section. So instead of the pump section dropping 6″ or more, the whole sump drops by only about an inch or two usually. Siliconed on the pump side of this baffle is eggcrate (found in the lighting department at Home Depot and some other hardware stores). On the K2 media side of the eggcrate is plastic mesh (needlepoint canvas which can be found in any craft store). The plastic mesh should be zip tied to the eggcrate and extend up to about one inch or so from the trim of the tank.

Pump Section: The last section is the pump section and allows you to use any return pump you want to. I prefer Rio pumps because they are compact (leave more room in the rest of the sump for more media) and come with a built-in grate that doesn’t clog like foam but still very effectively keeps large debris and fish out. They are also easy to open, maintain, and clean since unlike most other pumps, they do not require a screwdriver.

Glass Lid: Just like in the saltwater sump design, a glass lid on a freshwater sump greatly helps to cut down on noise, evaporation, splash, and to prevent any equipment inside the stand from falling into the sump.

Standard Freshwater Sump Design:

Best freshwater sump design k2

Freshwater Sump with Fish Isolation Section:

Fish Isolation Section: This can be invaluable in many situations. Whether a fish is being picked on, picking on the other fish, or just stressed out because it is a new addition, the fish isolation section can be the perfect place to keep fish. By still being in the same system there is no need for acclimation when the fish goes in to or out of the fish isolation section. It also means that unlike a hospital tank there are no extra water changes, heaters, filters, etc. It accommodates all the potential problems involved with quarantine/hospital tanks (water quality, uncycled tank, uncycled filters, etc.) except actual biological isolation.

how to build a freshwater aquarium sump filter

Where to Get the Glass:

Call a few local glass shops. Many will charge $40 or more per piece, others will charge as little as $5-10 per piece. Call a few shops until you get one with reasonable prices. In my experience, larger shops are busy with big jobs so little stuff isn’t worth their time, so they will have higher prices. Smaller shops appreciate your business and are happy to do small jobs between their big jobs, so their pricing is better.

Actual Assembly:

The actual assembly of the sump is pretty straight forward as long as you plan everything out well. You will need to order your glass from a glass shop. Some may not work with such small orders, but most should be happy to cut the glass for you. They will also grind down the edges so you won’t slice your hand open. You should base your measurements on the INTERIOR width and height. The width should be 1/16″ less than the actual interior width. For example, if the actual interior width of the tank is 12 1/2″ then the baffles should all be 12 7/16″ wide. The 1/16″ should be enough wiggle room to actually get the baffle in the proper placement. Double check the dimensions of the baffles when you pick them up, I did have one cut at the wrong size by the glass shop once and that will definitely mess things up for you.

All baffles should be at least 1″ below the bottom of the top trim in order to leave a 1″ gap above any baffles. Most baffles will have other factors that determine their height. For example, the first baffle in a saltwater reef sump should be tall enough to keep the water level around the skimmer stable without the water in the skimmer section being too deep for the skimmer to function properly. You may need to place the skimmer on an eggcrate platform to maximize water depth in the sump while still allowing the skimmer to function properly. Some PVC and eggcrate are perfect for an easy skimmer platform.

The second baffle in the saltwater reef design should be 1″ off the bottom and 1″ below the top trim. So if the actual INTERIOR height of the tank is 15″ from the bottom glass to the bottom of the inside lip of the top trim then the baffle should be 13″ tall.

The baffles on either side of the refugium in the saltwater reef design should be 6″ tall. This is tall enough to keep the sand and macroalgae in without being so tall that they interfere with the flow of water. A strong return pump can lower the water level in a sump a lot and if the last section is too small it can start to pull air and require you to overfill the whole system. By keeping the height of these baffles lower the water level in most of the sump will go up and down, not just the water level in the last section, so you should never have a problem with a pump being too strong for your sump.

Have the eggcrate cut to fit and ready to go as well, you will be using silicone to seal that in just like the baffles. I usually try to have it about as high as I expect the water level to be. You want it high enough to support the needlepoint canvas but low enough to be able to get the needlepoint canvas in and out.

Once everything is cut and ready to go and the glass on the tank is marked for exactly where you want the baffles, it is time to actually seal everything in. Silicone is only about $4-5 per tube so be liberal with it. The last thing you want is to be sparing with it and end up knocking a baffle out on accident once you already have the tank running. You can finish the silicone with ProCaulk if you want, it will look better. Let the silicone fully cure before you move the tank. Check that the baffles are placed properly and level, sometimes they will lean so you will want to correct this while the silicone is still wet.

The needlepoint canvas (plastic mesh) can be found at any craft store. Walmart also (sometimes) sells packs of it in their craft section.

The eggcrate is the plastic grid that goes over some lights. I have only been able to find it at Home Depot (not Lowe’s unfortunately). It is in the lighting section (near all the 4′ utility type light fixtures).

If you have any questions feel free to email me. I know that planning and building your own sump can be overwhelming so I am happy to help as much as I can.

Update: An Upgrade to the Sump on my 300 Gallon Freshwater Tank

making an aquarium sump

K2 Tumbling:

Three Types of Overflows:

How Sumps Work (Without Flooding):