40 Gallon Breeder Reef Sump Plans

This is my DIY Sump. It is installed under my 150 gal reef tank in a cabinet stand.

This design has been in use for over 3 years now, and there isn’t really anything I would change. It is about as simple as it can be.

I recently removed the sump from the system to clean it, and took some photos.

40 breeder reef sump plans baffle sizes


The sump is made from a new 40 breeder aquarium. It is an Aqueon brand that I bought from Petco as part of their “$1 per gallon” sale.


Large Return Section – This is one of the nicest things to have in a sump design. The return pump can be turned off and the return chamber will hold all the water that drains from the overflow box and display. The skimmer will not overflow due to the water level raising past it’s limit. So I never have to worry about turning off the skimmer for any reason during maintenance.

Minimal Baffles – there is only a 2″ wide space in the middle that is lost to having a bubble trap. Many sumps lose much of their available real estate to having too many baffles.


No weir on skimmer section – This means the water won’t be surface skimmed, and might start to accumulate scum. This was fixed with the addition of a pipe at the end of the post.

Turnover Ratings

My Mag 7 return pump pushes around 550 GPH with my 6′ of head height. The sump runs totally silent and has no sound from trickling or splashing. If you have a higher turnover rate, then noise will be heard first around the filter sock area. This is due to the narrow 6″ weir in that area. This design could run up to about 900 GPH without too much noise, just not totally silent.


The baffles are all 1/4” glass taken from an old aquarium I dismantled. The filter sock tray is made from 1/2″ HDPE plastic (more info below).

Building your own version

One thing to note – this is a general guide when it comes to measurements. While the height of each panel can be copied directly, the width may change in your case.  You will have to get your own tank’s exact measurements, and make any adjustments necessary. This is due to the fact that aquariums are made by hand, and every tank may be slightly different.

Check out the Reef Tank Sump DIY Guide for help with construction. It shows how to properly measure and cut panels. It also shows how to set up and then silicone them into place.

Baffle heights 40 gal sump reef tank

Baffle Heights

The 12” baffle (the last one in the series) sets the height of the skimmer chamber’s water level.

The sump holds as much water as possible during normal operation (about 25 gallons), while still allowing for drainage when the return pump is shut off.

If you are trying to design your own sump, and figure out what size and height to make sump baffles, look to the Sump Design page.

baffle construction reef tank sump


The notches cut in the bottom corners of the baffles allow water to pass under, similar to a raised baffle.

These seem to work well for this tank at the size I made them, however if made slightly smaller they would still work fine.

To see how I cut them, go to the Sump Baffles Construction page.

Bubble Trap

This sump has an under-over series of 2 baffles. This is sufficient at getting rid of the small amount of bubbles that the skimmer occasionally produces (such as when it is cleaned – but only for a day or so). While often seen, 3-Baffle bubble traps are unnecessary and just take up a lot of room. Long weirs and slow flow work best.

Filter Sock Tray

There is a filter sock tray that holds 2 X 4″ filter socks (mine are 200 micron mesh type). The tray is made with 1/2″ HDPE plastic (aka Starboard).

The tray was first cut on the table saw to size, then a router was used to create the rabbet notches on each end. You could also just do a few passes with the table saw to remove the material.

I also used my router to remove some material so the water flows down into the socks better without getting hung up on the “lip” of the socks. This isn’t totally necessary, but it does work better to keep it quiet.

sump design filter socks tray In the the original photo it was difficult to see the shape – I have traced over the edges in Photoshop to show the profile.

With this design, the tray needs to fit tightly. It should not allow any water to bypass the socks.

If the socks get too dirty, water will just flow over the wall to the next chamber.

Whenever you are making a piece like this, it is always a good idea to make a test piece first. That way you figure out your dimensions before you cut your “good” material.

filter sock tray design sump This piece of glass siliconed to the tank simply gives the tray a place to rest on. It’s dimensions don’t matter much.

filter sock tray Again, the shape is a little hard to see so I have traced over the image to better show the rabbet on the front edge.

The holes were first cut with a hole saw drill attachment.  I chose the bit that made a hole slightly smaller than what I needed. I then used my handheld router with a straight bit to inch up the size of each hole, a little at a time. I had a sock on hand to test fit as I went along.  This made for a snug fit for the socks so they can’t float up.

Filter socks in sump The notch on the panel shown allows for the chamber to overflow into the skimmer chamber if the socks clog up.

40 breeder sump under display tankThe sump placed back in the cabinet and filled up. Left to right: Skimmer, Skimmate Container, Heater, ATO sensor, Return Pump, and a Powerhead in the right corner.

Modification to First Chamber

One caveat to only having the baffles in an “under-over” setup is having no weir. This means it won’t surface skim from the first chamber where the skimmer sits. This wasn’t a big deal for the most part because I added a power head to that chamber. This helped reduce surface scum.

After I added a Nitrate reactor to the sump, I was getting a bit more slime and bacteria buildup in the first chamber.

I had thought about adding another baffle to act as a weir. This would have worked well, but I would have lost room in that chamber. It is already quite full with the skimmer and reactor in there. Draining the sump for a week didn’t seem that attractive either.

This surface skimming pipe was the solution. It uses a similar concept to an older protein skimmer design with the use of the wedge pipe. This allows you to adjust the amount of water passing through.

It’s a simple design with 3 parts:

  • A piece of flattened PVC to cover the existing opening in the baffle.
  • a piece of 1.5″ PVC pipe cut at an angle. It was sanded enough to fit in the Tee fitting, with enough clearance to turn freely.
  • a Tee fitting. trimmed on the bottom to form a base with the bottom of the plate

The plate covering the opening doesn’t create a perfect seal. A small amount of water passes around the plate. This is the reason it works.

If it was a perfect seal with a single pipe, then it would act as an open drain. This means it would constantly trip into siphon mode, and create noise.

Reef Tank Sump DIY Glass Baffles Guide

Reef aquarium sumps are easy to build with an existing tank and some spare glass. This post goes over how to do the actual work of construction. If you are looking to learn how a basic sump works, or how high to make the baffles, there is another page for that here: Reef Aquarium Sump Tank Design

What is in this guide?

  • Test fitting equipment and design with a mockup
  • Choosing the right thickness of glass
  • Where to find glass for cheap
  • Getting exact measurements for your cuts
  • Cutting the baffles and dulling the sharp edges
  • Silicone prep work – cleaning and taping
  • Clamping and supporting the baffles during glue up
  • Silicone application techniques

What’s not?

Once you figure out what water level you need in each chamber, you will be ready for this guide. We’ll go over how to carefully measure the baffles for the right fit. After prep work and cutting the glass pieces, you can start on actual assembly.

DIY sumps don’t have to be sloppy

You don’t have to shell out hundreds to get a sump that looks good. While it’s a little more work, you can build a decent looking sump with your own two hands. This guide goes over the methods to make it happen.

Getting good results

You may have seen some sump building videos on YouTube. There are quite a few. Many of the the people that make them seem to care about showing how fast they can do it, rather than doing a good job. They often end up with silicone gobbed all over the place or with baffles that leak and have to be redone anyway.

One thing you often hear people say about sumps is “small leaks aren’t a huge deal” and that sort of thing. This is not true.

If you have an unintended leak between baffles or dividers, it can cause problems. These problems may take a while to show themselves, say with an ATO sensor. It’s best just to do a good job with your seals the first time. Leak test the sump as you would any other part of your system.

Silicone Injection Method

The methods in this guide are some of the same ones used by professional tank builders. First, the tank and panels are taped and prepped. After that, the baffles are bolstered into position. This is usually done with clamps on the edge of the tank holding small blocks of wood. Next, silicone is injected into the gaps. After smoothing, the result is a continuous bubble-free seam. Applying the silicone in one quick process prevents it from “skinning over.” This is when the outer layer begins the curing process and begins to toughen.

Professionals all have their own tricks of the trade, but this guide gives an outline of a way to copy them. It is not the only way to do it, but it results in far less air bubbles in the seams than other methods I have tried.

Starting out

Once you have planned out your sump and know the rough dimensions, you will want to come up with your final dimensions for each piece.

Getting final dimensions for Baffles and Dividers

How to Measure – Allow about 1/16″ (1.5mm) to 1/8″ (3mm) gaps where the baffles touch the walls of the tank. This allows you to inject the silicone so it flows in the gap and creates a continuous seal between the two pieces. A gap closer to 1/8″ (3mm) allows the silicone to flow easier into the gap, if it’s too narrow, it becomes harder to inject in the opening.

For example, if you are measuring for a full-width panel that spans the tank front to back, here is what to do.

Say the inside measurement of the tank is 10″ wide. You would minus the 1/8″ gap from each side, adding up to 1/4″. Subtract that from the measurement and the resulting panel needed would be 9-3/4″ wide.

Apart from creating a good seal, the gap is left to avoid having to force or wedge a panel to fit which you should never do. While it doesn’t have to be too exact, it is better to have it a little loose than too tight. The silicone will fill gaps up to about 3/8″.

Spacers of the proper thickness will come in handy for this. Some people use zip ties or small pieces of plastic. In this build I used some rigid straws. The spacers on the sides can be removed as you fill the gaps with silicone. The spacers on the bottom should stay for about 45 minutes to an hour to prevent the weight of the panel from squeezing the silicone out from the bottom seal. You may also want to affix very small spacers to the bottom of the piece that will be permanently in there.

Planning your assembly

Test fitting

Once you calculate your final measurements, it’s helpful to do a mockup with cardboard. Just cut the pieces with a box cutter and tape them in the aquarium. This little extra step allows you to check a few things and identify any spacing problems with things like your skimmer or other equipment that might not be as evident on paper.

It might seem unnecessary, but this does a couple things for you.

  • Once you cut a piece of glass, you can’t really just shave a quarter inch off it if you make a mistake. You get one shot or you must start over using a new piece.
  • It’s nice to lay out the footprint of where everything is going to go. You might discover a piece of equipment won’t squeeze into a chamber like you intended. You’ll also find out what areas will be hard to access with your hands (say for cleaning or netting out fish).

Once you do this test fitting and you know how big to make the panels, you can either cut them yourself or take your order to a local glass shop.

Selecting the Right Glass Thickness

You will need your baffles to have some strength. Strong panels will stand up to being knocked around a little. When you are trying to wrestle a piece of equipment out of there while hunched over the sump, you aren’t thinking about being careful. Even doing some aggressive scraping of the glass will test them a bit.

Aside from not breaking easily, thicker glass prevents flexing or bowing from water pressure.

The point is this – a broken baffle in a full sump is no fun. It means draining, drying, scraping, and all of the hassle that comes from having your sump offline for enough time to re-cure new silicone.

Using 1/4″ (6mm) glass is what you should aim for for thickness. Quarter inch glass is also sometimes called plate glass. If you can’t find glass this thick, you might resort to something around 3/16″ (4.5mm), but that’s about the minimum.

1/8″ (3mm) glass is easy to find at home improvement stores. It is too brittle and you should avoid it.

A good source of glass is from an old tank. You can buy one for cheap. There are a lot of tanks on Craigslist or in second hand stores.

If you are looking at taking the glass from an old aquarium, start looking at tanks sized 29-35 gallons and up. Glass of at least 3/16″ (4.5mm) is found on these tanks. It can be a bit of work to dismantle a tank with razors and some wire, but you can potentially save a lot of money. Glass shops can charge a lot money for custom cut panels.

What type of Silicone?

Use a brand of silicone that is right for the job. Whatever brand you choose, you must ensure that the one you choose does not have any mildew-resisting chemicals in it such as brands made for use bathrooms and kitchens. There are a lot of types of silicone available at your local hardware store but they are all low grade sealants rather than adhesives. The easiest thing to do is just to get the good stuff from Amazon instead of trying to save $5. A good brand is “GE SCS1200” which has very good strength and about 15 minutes of working time. It is often recommended by professional tank builders and what is used in the build shown in this post. Another brand that gets recommended a lot is “Momentive RTV103”.

A single tube of silicone should be enough for 4-5 baffles. On this 40 gal sump I used 3/4 of a tube.


Cutting Glass Pieces

Using a standard glass cutting tool and a straight edge, the piece should be scored with a nice clean motion. Never go over the same score twice as it will dull the cutting wheel. It is worth it to do a little research on YouTube on the proper technique for this, but I won’t get into it here.

Roughing and shaping the panels

The edges of a newly-cut piece of glass can be extremely sharp. Edges should be ground with a sharpening stone or sanding block just to take off that sharp edge. Dulled edges will make it safe to reach in the sump with your hands and arms. If you are having a glass shop cut your panels, they can polish the edges but you really just need to dull them down. Wear gloves when sanding or grinding the glass.

Panels that sit on the bottom will rest on the silicone of the existing tank. This something we need to be careful of because the newly cut piece may have very sharp corners. It’s a good idea to nip the corners and sand them with the sharpening stone just so you don’t mess with the seal on the existing tank too much.

Cleaning the Glass

After cutting and sanding the edges, it’s time for prep on the pieces. You can start with wiping down the pieces with just water and some paper towel to clean them up a bit.

If you are using repurposed glass, you need to do a good job getting the pieces clean enough to get good adhesion. This is mostly important on the areas that will be bonded near the edges.

Parts of the glass that will be covered with silicone should be scraped with a razor blade and cleaned with Acetone (nail polish remover) or Rubbing Alcohol on a paper towel. It’s a good idea to take your time with this step and do a good job. This will remove any old silicone and clear off fingerprints for the best possible bond.

Installing Panels and Baffles in a Sump

In the sump design post I show water moving from one end of the tank to the other, flowing from chamber to chamber like a waterfall. This is done to make the concept simple to explain and show.

Most sumps you see are designed very simply – by placing a few rectangular baffles in there that span the width of the tank. Nothing wrong with this, it’s the easiest way.

One thing to note however — while you can’t really form glass into whatever shape you want, you aren’t just stuck with rectangles either.

There is a lot more you can do with a sump when you realize this.

Creating openings for water to pass through makes it so you don’t need too many baffles. Fewer baffles means you save space. Cutting a notch in the corner of a baffle is one technique you can do, and this is how to do it.

Cutting a Notch in a Corner of a Glass Panel

This method shows how to create a corner notch in a glass baffle. First drill a hole, then make relief cuts to remove the material you want. More info about how to drill glass is on this page: Drilling Holes in Glass Aquarium Tanks

Here is a video showing cutting a corner notch with the same technique but with better tools and results. It is easier to get a good clean hole without chip-out with thicker glass.

Here is where a hole has been cut too close to the edge of the glass. Hard to see in the picture, but a crack has formed between the hole and the closest edge. In this case it is what we want, but it illustrates why you need to have adequate clearance when drilling glass near an edge.

Relief cuts can be scored and snapped from the edges of the hole.

Once the snapping has been done, small bits of material can be removed with pliers or a wrench. This will result in a slightly jagged edge that may look a little rough, but can be sanded slightly with a sharpening stone. Heck, even a rock will do.

Securing Panels and Final Preparations

In this example I am showing the process I followed on a brand new 40 breeder. I got the glass for the dividers from an older 35 gallon that I cut apart (3/16″ or 4.5mm thickness).

It is handy to have some scrap wood to help secure the pieces as you work on them. Wood blocks secured with clamps will help to hold the panel you are working on. Spacers placed around the edges will help to create the proper gap (1/8″ or 3mm) around the piece.

Taking a little more time to secure the panels with spacers and wood blocks might add time to each step, but you’ll be glad you did. Silicone that has high strength has less working time than you might be used to, and you want to apply it in a quick deliberate process.

Smoothing and Removing Tape

Taking time to prep each seam will result in a much nicer end result. Each panel can be taped off along with the edges of the tank (as shown). After applying the silicone and smoothing it with your tool, remove the tape right away while the silicone is still wet.

Applying Silicone

During the few minutes of time when you are applying the silicone, you will learn a lot. Your preparation with taping and securing the glass panels will be evident.

The amount of silicone needed can vary. It depends on how you measured and cut your panels. For example, if you made the gaps between the existing tank and the edges of the panels larger, then more silicone will be needed. The target is about 3mm or 1/8″, so with a larger gap than that, you will be pumping the gun more.

If you only left a very small gap to fill (say less than the target of 3mm or 1/8″), less silicone is required. This may make it more difficult to get a good seam however, because the tube’s tip will have to be pressed firmer into the joint as you squeeze it out. This might make you work slower, and the silicone will get tacky as you use up the working time.

The way you cut the tip of the tube can also affect the process a lot. Some people cut the opening at an angle and then clench it with pliers to make it flatter. A lot of it is personal preference.

If you are working with a panel that is close to another such as a bubble trap, then you’ll only be able to apply the silicone from one side of the joint. In this case, you want the silicone to easily flow through the joint when it’s squeezed in from only one side. A proper sized gap (closer to 3mm or 1/8″) would be helpful in this situation to get the silicone to create a continuous seam.

Applying silicone needs to be done swiftly to get nice looking results. There are too many techniques and concepts to describe fully, and tank building is a skilled art. Experience will teach you more than reading tips and tricks ever will.

Curing time

It is very important to let the silicone cure for at least 7 days. 2 weeks if possible. This is done to protect your system from the effects of off gassing in the curing process.


You will discover many tips and tricks of your own as you work. Your 2nd sump with probably turn out better than your first. You will probably realize this is one trade where experience really counts.

Reef Aquarium Sump Tank Design

Reef Aquarium Sumps are something that can be very simple and easy to set up if you know a few things about what you are trying to do.

A big reason why sumps are confusing to beginners is that a lot of people make them way more complicated than they need to be. They see all kinds of pipes going all over the place and think they must be hard to build.

Depending on the stand or cabinet you are using, it can be a hassle to remove or change your sump setup. It is worth putting some thought into how you are going to use it and what it needs to do.

Sumps are simple, and you can turn a $20 Craigslist tank into one that functions just as well as $300 commercial models. This article will go over what I think is the simplest method to set up a sump in a bare tank, with all the reasons behind the design.

What are the main benefits of running a sump?

  • act as a buffer-zone where water moves to be filtered mechanically and chemically
  • slowly process water in such a way that promotes stability of the water and avoids spikes in water chemistry and temperature
  • let you run equipment out of view, so you can have a clutter-free display
  • contain any leaks from equipment or reactors from reaching the cabinet or floor

What we’re trying to do here

  • catch the water from the overflow drain outlet
  • deliver water to the equipment that processes it
  • remove any microbubbles that may have been generated by the equipment
  • return the water to the aquarium as quietly as possible

But we also want to make sure we:

  • have enough room to deal with back-siphoned water when the return pump turns off
  • have fail-safes in place where possible to prevent floods
  • cooperate with the Herbie, Bean or “siphon-based” overflow designs

reef tank sump design

Size Considerations

Most of the time, you’ll want to have as big of a sump as you can fit in the area.

Having a larger sump just makes a few things easier and less complicated. A bit of extra room to work with means being able to run just about any equipment you want. It’s nice to have some space available for extra live rock, reactors, and those sort of things.

The 3-chamber design shown in this article will work for the majority of larger sumps. If a small tank must be used – say 10-20 gallons – then you will probably have to alter the design and not use the center chamber. With a small sump, a 2-chamber design will allow the return pump chamber to hold enough water.

How much turnover should we have?

There are not many benefits to running high rates of turnover through your sump, other than having more water pass through mechanical filtration. Each individual piece of equipment processes water at it’s own rate, but most can process a very small amount at a time. For that reason I generally recommend a rate around 5X-7X of the display volume per hour. More on turnover rate here: What is the right turnover rate for a reef tank?

1st Stage – Where water from the overflow drains into the sump

The first chamber will have the highest water level and then cascade down to the other ones. For the first divider, you want the water to pass over a weir of some kind.

The reason for having water go over a wier is to maintain a consistent water level in the first chamber.

A consistent water level is something we need for the skimmer to work problem-free, and it’s also helpful if you have a siphon-based overflow. In order for the siphon to start, the outlet of the pipe must be submerged, but only by about 1″ (3cm) below the water surface. A siphon can’t start correctly otherwise.

Designing for your Skimmer

Most new skimmers available are non-recirculating models that operate in-sump. They usually have a recommended water height from the manufacturer they are designed to work at. This is usually at between 7-12 inches of water…

When a skimmer is dialed-in and properly adjusted, it’s pretty touchy. If the surrounding water level in the chamber rises, it reacts by overflowing the collection cup and skimmate collector. Not fun to clean up.

If you design this chamber to have all the water flow to the next one by passing over a weir, this won’t happen.

So if you are trying to figure out how tall to make the divider between this first chamber and the next, you may want to choose something close to 12″. You can boost a skimmer up to the right height with a DIY stand of some kind, but you can’t lower it if it’s already too high…

Having ample water depth in the first chamber gives you options. It allows you to change or upgrade your skimmer, just by adjusting the height of the platform.

Dealing with Back-Siphoning

When the return pump is turned off, gravity will cause the water currently being pumped up to the tank to fall back down. This means the sump will start filling up a bit.

The water comes from a few places. First, the water in the display tank will flow back through the return. Second, the water inside the overflow will drain. Lastly, some water from inside the pipes will drain down.

When added together, this can add up to several gallons of water flowing down to the sump.

There are ways to reduce this amount of water by correctly designing your Return Line and Overflow System, but no matter what – there will always be some back-siphoning of water.

This is why it’s nice to have a bit of elbow room when it comes to your sump’s capacity.

Ways to Minimize Drainage

Before we even get to planning out the layout of the sump, it is beneficial to reduce the amount of water that back-siphons and drains into it.

This is done by:

  • Return line outlet only submerged the minimum amount below the surface of the display tank.
  • Correct height of standpipes in overflow box – water will drain to level of lowest inlet in the box when the return pump shuts off.

Stage 2 – Housing Equipment (Optional)

The middle chamber of the design can have many uses. This can be an area for reactors, heaters, or anything else. Hanging lighting over the area for a frag rack or refugium area is also common. You will most likely want a constant water level in this chamber too. This avoids the risk of having pumps or heaters running dry from a low water level.

Return Pump Chamber – Where the water level fluctuates

Your return pump goes in the last stage of your sump, how ever many chambers that ends up being. The water level here will lower as water evaporates, and raise when you top off the system with fresh water. So some people will mark the glass to show what the water level is supposed to be at when the system is topped off.

A piece of masking tape to indicate the high water mark can be helpful. Make sure that when you mark this point, the return pump has been shut off and all water has collected in the sump from the overflow and return line… That is the true high point.

Making sure the sump doesn’t overflow

By designing the sump to have water flow over a series of weirs, we control where the the water level will change. As it falls from chamber to chamber, it will collect at the end. This last chamber’s water level will vary based on evaporation or top-offs.

So this means all the other chambers up the river (the ones where water passes over a weir) will remain consistent.

A cause of frustration among first-time sump builders is overfilling. It is often not discovered until the plumbing is done and the return pump is turned on, then turned off.

It can be tempting to make your return pump chamber very small, because that is probably the only piece of equipment that is going in there. Might as well make lots of room for the other chambers, right?

This can have unintended consequences, which I’ll explain.

When the return pump shuts off, gravity takes over. Water will start to drain from the overflow box, display tank, and inside the plumbing. All this water collects in the return pump chamber. If it can’t handle the volume, the water will fill the other chambers upriver. This can result in the skimmer overflowing or in the worst case the whole sump.

Overfilling when the return pump is shut off is the result of a simple problem — The chamber where it resides is too small.

Contrary to many sumps you have seen, the return pump chamber will often be the largest chamber in the sump.

The good news is that overfilling due to back-siphoning is easy to avoid. By calculating the return pump chamber volume beforehand, we can estimate how big it needs to be in the planning stage.

Determining Return Pump Chamber Size

First, we know that the return pump rests on the bottom of the sump.

It’s meant to be fully submerged, so we need at least the height of the pump itself as a minimum water level.

As the water evaporates from the system, the water level falls in this chamber. So at a certain point, the water level will get low enough that air starts to get sucked in.

If this happens, a loud slurping sound will be heard.

The typical pump won’t slurp air unless the water level is very near the inlet. So you need 2-3″ of water above it to prevent this from happening.

Figuring out how much water needs to be in there to keep from sucking in air gives you a baseline. This baseline will be where you can start measuring the volume of the extra capacity needed for drainage. This baseline water level will be also be close to the normal operating level of the chamber — while the return pump is on.

For example, in this case we will say that 6″ of water is the minimum water level that a return pump can operate without it starting to suck in air.

Above the 6″ mark will be the base of our needed “extra capacity.”

sump drainage capacity

Calculating Extra Capacity or for when the return pump is shut off and the system comes to rest

There will be a few gallons of water that drains down from these sources:

  1. Overflow box (drains to lowest inlet or standpipe)
  2. Display tank – the amount of water between the height of bottom of overflow weir and the height of the lowest point of the return outlet (usually only about 1/2″ of depth if you design it right)
  3. Inside the pipes (not much water unless using long runs of pipe)

So by adding these three sources together, we calculate the extra capacity needed when the pump shuts off. In the case of the overflow box and display water, the volume is easily calculated with L X W X H.

When the extra capacity is added to the minimum, we find out the total required capacity of the return pump chamber.


Even if you decide to forgo these calculations and just use a check valve, there is another issue with creating a return pump chamber that’s too tiny. There will be a lot of swing in the water level height. This means that the water level in that chamber will rapidly go down as water evaporates from the system, and rapidly rise when the return pump is shut off and water empties from the pipes…

So why does this matter?

Well if you are using an ATO (and you should for many reasons), then you will want it to top up the system a few times per day, but no more than that. If the chamber’s volume is too small, then the ATO’s sensor will trip constantly — possibly shortening the unit or pump’s life from overuse.

For this reason you might want to make your return pump chamber larger, just to avoid this excessive swing in water level height.

Teeing Off the flow of the Return

Some people will use their return pump to also feed the refugium or one or more reactors. This means they they Tee off the return line and direct some of the flow over to that equipment.

A downside to Teeing off the return to feed either a skimmer or a reactor is that it will affect the return rate up to the display.

The return rate affects the overflow. If you have a siphon-based overflow like a Herbie or Bean Overflow, then variations in flow will mean re-adjusting the valve. This can be annoying to have to do all the time.

These variations in small amounts of flow is one reason why the Bean Overflow design has an advantage over a Herbie design. The Bean has the ability to take on variances in the rate of flow through it’s open channel, where the Herbie would need to have the valve adjusted.

So if you’ve got a siphon-based overflow, the system works best if the return pump’s only job is to push water up to the display. The flow may be Tee’d off to provide flow to something that provides consistent pressure such as a refugium chamber, however diverting flow to a manifold to power media reactors generally doesn’t work well with a siphon based drain. This is personal preference because most people don’t want to deal with frequent adjustments.

Sump Construction

caulking gun

The dividers of a sump are called Baffles — vertical panels siliconed in place. The configuration of the baffles determines how the water flows from chamber to chamber.

In a glass sump, you should use glass baffles. Using silicone to affix acrylic panels to glass doesn’t work well in general as it will never create the same strong permanent bond as silicone to glass.

Dealing with Microbubbles

Tiny bubbles in the water are called “Microbubbles” and will blow around in the current of the water column, until eventually bursting at the surface. While they are harmless, they can detract from the crystal-clear look of the water. Common sources can be skimmers and overflow pipes, or anywhere water falls more than a few inches.

Bubble Traps are a series of 3 baffles placed one after another to ensure all the tiny bubbles dissipate. They work by moving the water vertically up and over a barrier where water is calm.

While they work well, they can take up a lot of room in the sump. If you don’t have a lot of room to work with, you might want to skip using a bubble trap. Most newer skimmers don’t produce many microbubbles at all, especially once broken in. Placing the skimmer near the drain line outlets on the opposite end of the return pump should create enough distance in order the for bubbles to pop before they make their way to the display. While not needed in every circumstance, it’s nice to have a bubble trap in place just in case you need it one day.

Building a Bubble Trap


Bubble traps are usually placed at the last divider before the return pump chamber. This way bubbles dissipate before getting pumped back up to the display tank.

Distance Between Baffles

As a general rule, the baffles in a bubble trap should never be closer than 1″ (3cm) to one another.

If you are passing water underneath a baffle, the panel should be raised off the glass the same distance. The height of the opening should be at least equal to the gap between individual baffles. This will avoid a bottleneck in flow.

While it may be the norm to only have 1 inch of space between baffles, it is really the bare minimum.

A gap of only 1" creates an area that is hard to access. A larger opening will be easier to clean between the panels. Furthermore, if you keep livestock in the sump, it can be a real pain to net something out from between 2 baffles if they are only 1" apart.

A gap size of 2" is often better, not to mention easier to install in the construction phase. By creating more space between the baffles, you promote stillness in the water. Stillness helps bubbles rise to the surface.

Under or Over?

The diagrams on this page show Under-Over-Under. Designing a bubble trap with this pattern is less common. There is no wrong way, but I find the Under-Over-Under way has a few benefits.

If you make the bubble trap the opposite way – as Over-Under-Over, it creates an area that is hard to access.

Over time, some detritus will settle at the bottom of an Over-Under-Over bubble trap. Not a big deal to most people, but if you want to clean out that part, it can be difficult. The space at the bottom is almost impossible to access.

Also – if you keep fish in your sump from time to time as I sometimes do – Over-Under-Over bubble trap can be a pitfall. If a fish gets in the middle – you will have a hell of a time getting it out.

Under-over means you will create an area that won’t get surface skimmed and could be more stagnant. This stagnation can be countered with a powerhead in that chamber.

So both configurations have pro’s and cons, but it’s personal preference.

Either way of setting up a bubble trap will keep microbubbles away from the return pump. Ultimately, a slow rate of flow is the biggest factor in how well they work.

Installing Baffles in a Tank

There are many steps involved in selecting and preparing your glass baffles. This info has been split into it’s own post: Reef Tank Sumps: DIY and Construction

Things like measuring, cutting, glass thickness and prep work are shown. There are photos of a 40 breeder sump build with some helpful DIY techniques for working with glass and assembling the sump.

Refugiums and Sump Setups

Some people will install a refugium into their sump. While common, there are plenty of people that just do without them. The term itself has become a little generic. A “Fuge” often just refers to an area of the sump where there is lighting and stuff grows.

What is the Sump actually doing?

A repeated statement in reefkeeping information is that your refugium needs slow flow running through it. This is not true in all cases.

Some people will Tee off the return pump and divert a portion of the returned water to a “slow flow” chamber. Reducing flow like this is usually counter-productive if the refugium’s main job is to grow macroalgae.

Macroalgae grows the fastest with two things present. Good water flow (more oxygen) and lots of light in the proper spectrum. Reduced flow will just impede it’s growth.

So the question is, why bother Teeing the return line?

It is simple to just place the macroalgae in a sump chamber with consistent water height. Usually the macroalgae needs to be segregated or prevented from getting sucked into pumps. A plastic mesh divider or basket can be used in these cases.

Some refugiums are created as a habitat for microfauna and all the critters that live in the reef. These area are a true “refuge” and will usually have some kind of sandbed. Providing a safe place away from fish and predators will theoretically let them flourish and multiply. The ideal amount of flow for these types of refugium zones is a matter of debate and many people have tried to experiment with them but there isn’t really a consensus.

If you are building your first sump then you will probably get the most mileage out of trying your hand at growing macroalgae like Chaeto. A more complicated refugium setup can then be something you choose to experiment with or forgo altogether.

More advanced designs

In the diagram at the top of this article, I show water moving from one end of the tank to the other. The water cascades, flowing from chamber to chamber like a waterfall. Illustrating the concept this way is simply done to make the concept easy to explain and show.

This design is generally a good practice. When the dividers span the whole width of the tank (front to back), the water passes over a longer weir. Having water pass over a longer weir allows for slower flow that is quieter.

Sometimes you want to go a little further with your design. In order to maximize what the sump can do, having each divider span the full width of the tank isn’t always the answer. More creative and intricate sump designs are possible. Rather than just having rectangular pieces of glass, you can create openings for water to pass through.

Cutting notched panels with the corner cut out allows for the sump to do a lot more with the minimum amount of dividers. For an example of this check out the Reef Tank Sump DIY Construction post or the 40 Breeder Sump Plans

Containing Spills and Being Proactive

Having a large sump with fairly high walls allows you to have a bit more piece of mind.

Equipment such as reactors have the potential to come apart and leak. The pump that drives them will continue to go, and can put water where you don’t want it.

Reactors may also have flimsy barbed fittings and tubing, especially on the cheaper models. If one of these fittings blows out, you want the reactor in a place where the water will only spill into the sump and not anywhere else.

The same also goes for things like a Skimmer’s Skimmate drainage Container. While common to be be located next to the sump, what is to happen if it overfills?

Anything with the potential to leak should ideally be located inside the walls of a sump or just above it. It can also be a good idea to install a water alarm in the cabinet.

There are many ways that a tank can potentially leak, which you should always be aware of. For this reason I have also written this post here: Common Causes of Flooding on Reef Tanks