What Are Aquarium Sumps?

A sump is a large container of water that exists outside of your aquarium that houses equipment that normally resides in the display tank. This can range from heaters, filters, and other mechanical needs all the way to refugiums, baffles and copepods.

In essence, an aquariums sump holds all the vital organs so that our display tanks can be clutter free and display only our beautiful aquascape.

Benefits Of A Sump

Building your own sump can be a lot of work, and buying them can be far more expensive than most purchases. Surely the benefits must be great right?

Just as you would expect, with so much going into building a sump you are guaranteed tank altering results.

Learn how to build your own sump here

Effects Of Increased Water Volume

Any aquarist will tell you how they wish they had a bigger tank. with every added gallon we:

The accepted rule is one inch of fish per gallon of water. By adding a twenty gallon sump to a fifty gallon tank, we increase the amount of fish allowed by 30%.

"Wait that math doesn't add up!" Very true, if our sumps were filled to the brim this would allow a 40% increase. So why are we selling sumps short? simple. When a sump is planned to be filled to the top, we leave no room for safety. This means if anything goes wrong, such as the return pump gives out, our sump will flood onto our nice floors. We will cover the process later but for now keep in mind the sump will not be filled to the top.

The nitrate cycle is the main reason, aside from feeding, that we cannot set and forget our aquariums. As you add food, your fish either eat the food and convert it into waste or miss the food and it rots into waste. Either way feeding fish creates waste in the tank.

Taking our previously found increase of 30% water into account, your aquarium will be able to go much longer without water changes.

But that's not all! In these sumps we place refugiums that help eat nitrate, the final product of the nitrate cycle, and slow the process even further. Again we will have to touch on this later in the article so stick around or jump down if you gotta know right now.

Salt creep: when salt accumulates on the top of your tank from water evaporation, and water evaporation itself are the two beasts of this problem. While sumps do not stop the two, they do slow the processes. Losing five gallons from our hypothetical 65 gallon combination is a loss of 7.7% of the systems water. With the tank alone this jumps to 10%. The smaller percentage will vastly reduce changes in water levels as well as salinity levels.

Quick and simple on this point. More water heats and cools much slower. A perfect solution for keeping your fish in their optimal temperatures.

How To Maximize Sump Benefits

While adding a sump without further specialization will help all tanks, you want to get the most out of your equipment. Use each section properly and your sump will take almost every aspect of care for the entire system onto itself.

Having a spot your fish cannot access is key for owners of copepod or brine shrimp dependent fish. These creatures are free to hide in the refugiums built in between the baffles of a sump, creating a safe breeding ground that will steadily supply your display tank with live food.

We have yet to meet an aquarist who likes the look of bulky aquarium equipment in their display tank. Removing hang on back filters, long heaters, protein skimmers and in tank aeration such as air stones create a much more natural setting.

Even better are the increases in effectiveness each part can gain from specific areas in your sump.


When new hobbyists have a 10 gallon tank, water changes are no issue. Simply siphon out water and then raise a bucket to pour new water in. This is fine because the tank is only ten inches tall. When you own a 300 gallon tank? Not so fine.

Sumps are located close to the ground for many reasons, almost to make your life easier. Water changes three feet off the ground are much easier than six feet on the ground, especially with five gallons of water weighing over forty pounds. Some people choose to solve this problem with multiple trips and buckets, increasing the time, materials used and adding user frustration.

With tanks large enough water changes switch from pouring to pumping. Pumps make water changes far easier by moving the water anywhere while you hold the tubing instead of the massive water bucket. The only downside to this is the pressure of the incoming water. Unexpected water flow startles fish, makes coral retract or fall over, and can disrupt your substrate. By pumping the water into the sump rather than the display tank, the inhabitants are none the wiser to our caring actions and can continue living in peace.

Bubbles can only cause trouble. Yes they do aerate your tank, but adding the risk of fish irritation, trapped air under ridges or rocks, and a massive increase to both evaporation and salt creep is not worth the bubbler.

So how does the sump provide aeration? Bubbles themselves do not add air to the tank, but the way they disturb the surface does. As your water flows down the siphon and into your sump, it crashes into the surface of the sumps water and creates more water surface disturbance. This gives your fish the oxygen they need to survive without all the harmful evaporation.

Decreasing water levels harms your tank in multiple ways. First the toxin concentration increases. Second the salinity level in marine tanks also increases. Both of these can stray into levels that become uninhabitable for fish.

But how can lowering water levels be so dangerous?

As fish waste collects in your tank, toxins build up until you can perform a water change. Normally this is not too dangerous and we have weeks to change the water. When your water level decreases, the ratio of water to toxins sharply falls while more toxins are constantly building. The number of toxins a 65 gallon tank can handle is far greater than that of a 50 gallon.

Sumps combat this problem efficiently, effectively and easily. As previously mentioned, the over all set up reduces evaporation with more practical aeration. The additional water volume lowers the percentage hit your tank suffers from evaporation, making your tank safer much longer. Lastly, the smaller surface area of a sump means the surface disturbance will cause less evaporation and salt creep than it would in your beautiful display tank.

By following all these steps you will see an immediate change in your tanks health. Brown algae will decrease, tank plants and even in some case fish will gain more color, and best of all you will save valuable time by lowering how often you must work to maintain the perfect aquarium