Basic Sump Components Sump with refugium

A sump is basically a container of water placed below your aquarium, used primarily to house filtration equipment. Whether your tank is large or small, we all know that one of the most precious commodities in our hobby is space. Although you can definitely get away with using minimal equipment on your tank, there is little argument that having filters and top-offs can make your aquarium journey much easier. Unfortunately, all of these tools can take up a fair amount of space and aren't always the prettiest. This is where the sump comes in.

Having a sump gives you the option of adding all sorts of equipment that would normally take space away from your aquascape and livestock while also being able to hide everything away, giving your tank a much cleaner look. A sump is especially important on larger tanks where hang on skimmers and reactors simply aren't large enough to provide adequate filtration.

The other major benefit of a sump is simply that it gives you more water. A larger water volume means the water chemistry won't change as fast and you have a bit more room for error. Thank to dilution, the point at which the water becomes concentrated with pollutants to dangerous levels just won't happen as fast as it happens in a smaller nano tank. 

Basic Sump Components

What Do You Put In A Sump?

A sump can really be as simple or as complicated as you want to make it. These components are found on a majority of sumps used on saltwater aquariums.  Your sump may look a little different but for the most part, these components function the same way, in every single sump out there. 

Filter Socks and Filter Rollers

A filter sock is a basic form of mechanical filtration. When the water first flows down into the sump, the plumbing will either lead into a chamber that fills the filter sock or feed into the filter sock itself. These socks come in different micron ratings and will filter out debris as the water passes through them. The smaller the micron rating, the smaller the holes in the filter and the smaller the debris that will be picked up. Socks should be changed out every 1 to 2 weeks depending on how dirty your system is and can either be washed or simply replaced with new ones. Pretty much every modern sump will come with a built-in filter sock holder, but for older or DIY sumps there are plenty of mounts that will let you add a filter sock to your filtration.

For those of us who don't swap out their filter socks as often as we should, installing an automatic filter roller may be what you need. This piece of equipment takes the place of a filter sock by utilizing a roll of filter sheet (kind of like toilet paper). When the portion of the filter roll begins to get clogged the auto filter roller's water sensor is triggered by rising water, automatically rolling in a new section of filter sheet. The unobstructed flow through the new section of filter sheet drops the water level, and the process repeats throughout the day. Be sure to swap out rolls as needed.

*Tip: Always rinse new filter socks before adding them to your sump. There is often residue left on the socks from the manufacturing process that can make your skimmer go crazy if not rinsed off.


There's really not too much to say about heaters. Fish need the water to be between certain temperatures to survive and a heater will help keep the water warm enough for them.

*Tip: Keep your heater in one of the chambers before the return chamber on your sump. If the water level drops in your tank, the first place it is going to drop is in the return chamber. If this is where your heater is you can run the risk of running it above the water level which can be hugely damaging to it.

Protein Skimmer

A protein skimmer is the heart of your tank's filtration and can be found in nearly every marine tank. A skimmer produces small air bubbles that attract biological waste. These bubbles then rise through the skimmer's body, spill over the top edge, and are then deposited in the collection cup once the bubbles pop. Without a protein skimmer, biological waste in tanks would get out of hand very quickly and maintaining tanks would be much more difficult.

*Tip: Your water level can be the key to your skimmer's success. If you find that the level is too high or too low, try adding or removing about an inch of water and observe for a day or two to see how the skimmer reacts. If you find that the level is too high, consider placing the skimmer on a skimmer stand to maximize its efficiency.

Eshopps Sumps
  1. AR-300 Aqua-Fuge Refugium Sump 4th Gen
    AR-300 Aqua-Fuge Refugium Sump 4th Gen

  2. AR-200 Aqua-Fuge Refugium Sump 4th Gen
    AR-200 Aqua-Fuge Refugium Sump 4th Gen

  3. AF-300 Alpha Fuge Sump 4th Gen
    AF-300 Alpha Fuge Sump 4th Gen

  4. AF-200 Alpha Fuge Sump 4th Gen
    AF-200 Alpha Fuge Sump 4th Gen

  5. AF-100 Alpha-Fuge Sump 4th Gen
    AF-100 Alpha-Fuge Sump 4th Gen

  6. RS-300 Reef Sump 4th Gen
    RS-300 Reef Sump 4th Gen

  7. RS-200 Reef Sump 4th Gen
    RS-200 Reef Sump 4th Gen

  8. RS-100 Reef Sump 4th Gen
    RS-100 Reef Sump 4th Gen


Baffles and Bubble Traps

Baffles serve a number of purposes in sumps, the biggest of which is maintaining the water levels in the chambers leading up the return chamber. By having a baffle that reaches the bottom of the sump, it ensures that the only way for the water to escape is to pass over it. This means that if you have a 9" tall baffle, then the water level in the previous chamber must be at least 9" for the water to continue on.

The other major purpose of a baffle is simply to control the rate at which water moves through the sump. Being that a baffle is really no more than a short wall, water is obviously going to stop and settle when it hits it. This prevents the water from just flowing past your filtration and back into your tank without actually being cleaned.

These baffles will often be configured in what is called a bubble trap before it hits your return pump chamber. This is simply two baffles, the first of which reaches the bottom of your sump, and the second of which has an opening at the bottom. As the water flows over the first baffle at a higher level, it then is stopped again at the second. To pass by the second it must flow to the bottom of the baffle and move under it. Ideally, as the water moves down, any air bubbles suspended in it will rise to the top and be released instead of continuing to be carried by the flow. You will also sometimes find a pretty heavy sponge filter in between the baffles that can act as an extra line of defense and catch the bubbles as water passes through.

Return Pump

So I lied earlier. The protein skimmer is more like the liver or kidneys of your tank. The real heart is your return pump. Getting water into your sump is pretty easy as gravity will do 99% of the work for you. Unfortunately, gravity is not your friend when it comes to getting the water back into your tank. This is where the return pump comes in. The return pump's only job is to take water from the sump and put it back into the display. For sizing a return pump, the general rule is you want about 10 gallons per hour of flow for each gallon of water in your system, so if you have a 45 gallon tank, you are going to want at a pump that will give you at least 450gph of flow. Keep in mind that these desired numbers should also take into account head pressure so in most cases it's better to oversize the pump a bit or break out the calculator and find out exactly what size you will need.

*Tip: Just like with your actual heart, taking care of your return pump will extend its lifespan and improve its overall performance. It's a good idea to disassemble the pump and give it a quick soak in a water and vinegar solution to break down any calcium build up every 3-4 months.

Check Valve

Check valves are your friend. You won't need them often, but those few times you do, you'll be glad they're there. The basic function of a check valve is it only let water flow through it one way. The major place that these are installed on the return line, above the return pump. On the occasion that the power goes out or a pump fails, water will drain from your tank back into your sump until air is introduced into the line to break the siphon. Depending on the tank, this may only be a few gallons or it could be many many more. Either way it's not worth the risk or the mess and you should just install a check valve about your return pump.

*Tip: Pretty much every check valve will come with an arrow on it. Make sure that when you install it, the arrow is pointing the direction that you want the water to flow. If you have it pointing the other way, your return pump will basically just be pumping water straight into a wall and things aren't going to go well.

So that's about it for a bare-bones sump. You should definitely look into other products such as Auto Top Offs and Media Reactors to stuff your reefing game up further, but this is a good place to start.

What is a refugium?

A lot of sumps now days come with a space that can be used as a refugium. So what is a refugium? Refugiums, or fuges, can be thought of as a refuge and are basically areas for things that you don't want or can't have in your main display to thrive. This can be a variety of things, from a deep sand bed, to a breeding area for copepods, to being extra space for additional live rock. They can even be used as a grow-out area for new frags if you have the right lighting. Depending on the model of sump you have, this space may be in the middle of the sump, in which case it won't require any additional plumbing. Sometimes you will see the refugium on the far side of the sump, separated from everything else by the return pump chamber (These can also be used as ATO reservoirs). These types of fuges function a bit differently as you will need to T-Off of your main drain line to feed water into them. So let's see what can be found in a fuge!

Sump with refugium

Gate Valves

So a gate valve is actually before the fuge, but it's still very important for these side plumbed variations. Because you are generally keeping more delicate animals or plants in a refugium, you will want to make sure that the flow moving through it isn't too great to damage or disturb what you're sheltering. In the center sump fuges, this isn't an issue as the baffles will slow the water down before hitting it. On side plumbed fuges the water is coming directly from the drain meaning that it's going to create too great of a flow for your standard fuge. By placing a ball valve on the refugium side of the Tee, you can choke the water back by closing the valve a bit and slow the water to an appropriate speed.

Refugium Light

This one is pretty simple. One of the major uses of a refugium is to grow macroalgae (we'll get into the reason here in a second). Algaes are photosynthetic so they will need light to grow. Although most lights will work for growing algae to some degree, refugium specific lights are tuned into the ideal wavelengths for growth and will help to supercharge any algae in your refugium, given enough nutrients.

Macro Algae

Now that we went over the light, let's get back to the macroalgae. So just like algae in your display, macroalgae will grow when there are too many nutrients in your tank given enough light. The major difference between something like hair algae and most macroalgae is that macroalgae are easy to get rid of (and usually look cooler). Basically, all macroalgae are there to do is outcompete other algae in your tank for nutrients and starve them out. Once they've grown big enough, just harvest some of the algae from your refugium and dispose of it. What's left will then continue to eat the nutrients, grow, and then the cycle will repeat itself. Most people's go-to macroalgae is chaetomorpha as its easy to harvest and grows quickly, but there's a variety of other ones out there as well.

*Tip: If you're looking to grow copepods in your refugium, macroalgae is a great addition. Pods love to hide in the algae so you can easily grab a handful of chaeto and shake it into your tank if you're looking to seed them into your display.

Live Rock

So in a reef tank, there are two major parts of your natural biological filtration. The first major part is your liverock. Because of this, most people want to try to maximize the total amount of live rock in their tank to increase their biological load of nitrifying bacteria. Adding a refugium will simply give you a bit of extra real estate that can fit additional live rock. It also has the benefit of giving copepods an additional place to live and breed.

Substrate/Sand Bed

The second major part of your natural biofiltration is your sand bed. In your sand, aerobic bacteria will colonize the top several inches of the substrate to help with nitrification. Once you get down to about 4 inches where oxygen can't reach you will start to find anaerobic bacteria. These bacteria are great for denitrification which is awesome, but unfortunately, they are also great at producing hydrogen sulfide which is a toxic gas. Typically you wouldn't want such a deep sand bed in your display as you would be running the risk of disturbing it and releasing toxic gas into your display. Thankfully, in your refugium, you can safely keep a deep sand bed without the threat of the sand being disturbed, making this a great area to promote denitrification.

Rather than keeping a deep sand bed, you can also use a refugium substrate. The substrate grain size is specifically designed to provide the correct amount of surface area to promote a variety of bacterial growth.

The options for what you can add to a sump are only really limited by your imagination. If you are interested in getting a sump setup feel free to contact us and we would be happy to help out!