I think it’s fair to say that most aquarium hobbyists at one time or another had a standard aquarium, like a simple setup from Petco with a basic filter and a heater. My first saltwater reef aquarium was a 46g glass bowfront tank with a hang on back filter, a hearter, and a little maxi jet pump. As I became more involved with online forums and met other fellow reefers I was introduced to the concept of a “sump” and was intrigued by it and wanted to implement it as soon as possible. In this article we will discuss what a sump is and why to use it. If used correctly it could be used for saltwater or freshwater aquariums with much success and benefit.

What is a sump?

A “sump tank” or “sump” is simply another tank that resides under the display aquarium or at least somewhere lower than the aquarium. I should clarify that it doesn’t necessarily have to be a glass or acrylic tank – some people have used rubbermaid tubs or other plastic made containers – but for the purposes of this article we will assume the sump is a made of glass or acrylic. Using gravity, water flows into the sump from the display aquarium and to create a perfect balance, a pump that sits down in the sump pumps water back up the display aquarium. So…all we are trying to accomplish is a balance where water flows in and out of the aquarium display without overflowing the aquarium or the sump tank.

How water flows down to sump and up to the aquarium and how to balance it?

As mentioned above, the water flows down to the sump with the most dependable method of all – gravity! This is where the concept of an overflow is introduced and needs to be discussed briefly. An overflow is a separate box-like compartment that is either built into the aquarium internally or externally (otherwise known as “reef-ready”) or could be added as a “hang on back” device. This box has hole(s) where a bulkhead fitting it used and PVC or other types of tubing is used to send water down to the sump. The overflow box has slits or “overflow teeth” on top and will pull water from the top 1″-2″ of the display aquarium. The water now needs to flow back up to the display aquarium and is done so with an aquarium pump or what we call a “return pump”. As long as your plumbing is large enough, whatever the gallons-per-hour rating is on the pump (GPH) is what the gravity feed will match (head pressure needs to be calculated her as well and is provided by the pump manufacturer). In other words, the velocity of the water flowing is determined by the strength of the pump. It is always a good idea to use a check-valve on your pump to avoid a water siphon from he display and also only fill up the sump half way up or lower so there is room for water to flow down when power shuts off without overflowing the sump.

Benefits of a sump – remove eyesores from the display

One of the things that motivated me the most to implement a sump was my dissatisfaction of looking at equipment inside the aquarium display. I find heaters and pumps not so pretty to look at :) My first 46g reef aquarium had a heater, hang on back filter, and a circulation pump in the display accompanied by electrical cords showing in the aquarium – ughhh the horror! If you’re reading this I assume you feel the same! So, once you have a sump implemented, the heater(s) could be moved down into the sump. To avoid any circulation pumps, I added a device called a “seaswirl” which allowed the water from the sump to be directed to different parts of the display aquarium. The ugly part of the hang on back filter was now gone as well…combine all this with a black background in the aquarium and whatever nozzles are present are not very visible to the human eye – success! Love it!

Benefits of a sump – no more surface gunk

Maybe I’m a bit of a perfectionist, but another thing that bugged me with my first reef aquarium was the oil and gunk that accumulated at the water surface – I found it to be an eyesore and gave the tank a “dirty” feel. Once I had added a sump to my setup, the overflow box took care of this problem immediately by skimming the water surface 24/7 and sending all the gunk and oil down to the sump to be filtered out.

Benefits of a sump – better filtration

By skimming the water surface and sending water down in the sump we are now able to send water more effectively into a filter sock or filter pad for waste to be removed. This is much more effective than a hang on back or canister filter pulling water lower in the display. Furthermore, now that a sump is in place a protein skimmer could be implemented with huge benefits added to your filtration. Some hang on back protein skimmers do exist but they are not nearly as effective as in-sump ones. Other filtration devices could also be implemented in and around the sump such as refugiums, media reactors, UV sterilizers, etc.

Benefits of a sump – more oxygen

Because water is “crashing” down into the sump via gravity, oxygen is added to the water which is always a good thing :) Also, as mentioned in the previous section, a protein skimmer will not only be a great filtration device but will also introduce plenty of oxygen to the aquarium. This new source of oxygen will also help you keep the PH elevated to proper levels.

Benefits of a sump – increased water volume

Another great benefit of a sump that is often overlooked is simply the increase of your water volume. You will often hear that with aquariums bigger is better and that is definitely the case as bigger water volumes allow more stability and less fluctuations. Also a bigger volume can take on more waste than a smaller one. For example, let’s say you have a 100g aquarium with no sump. While out of town, a power outage takes place and the aquarium is shut off for a whole day. The aquarium is now susceptible to an unsafe increase or decrease in temperature (depending on the season) and an ammonia spike is inevitable if animals should start dying. Now, if the same setup had a 30g sump – the increased water volume will take longer to cool or heat and can take on more waste as the ratio of fish to water is lower.


As we’ve covered in the sections above, there are many benefits to adding a sump to your existing aquarium setup or when planning on a new aquarium. We highly recommend it and are confident that it would be of great benefit. It is worth mentioning that if the budget allows, an acrylic sump is best since it is easily modified and drilled. Also, an acrylic sump is safer to use as covered in previous articles. I hope this article has been helpful and informative and helps you with implementing a sump for your aquarium.