Sump Filtration for Saltwater Aquaria

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What is a Sump & Why use it on a Saltwater System?

Most aquaria will require some form of filtration. Nano tanks (under 35 gallons) might be able to squeak by with frequent water changes; however, all systems will dramatically benefit by the inclusion of filtration. There are several options on the market: canister filters, hang on back (HOB) filters & sumps. While each option arguably has its own benefits; a majority of saltwater aquarists rely upon sumps for their systems.

A sump is a tank typically housed beneath the main “show” aquarium. Sumps become an extension of the aquarium system as water from the show aquarium is drained to the sump for cleaning & treating before being returned to the main aquarium. The inclusion of a sump will increase the total water volume of the aquarium system, which in itself provides more stability for your aquatic residents.

​So why go with a sump? Saltwater systems can be adequately run with either canister filters or HOB filters. Our nano saltwater aquarium operated with a small canister filter for several months to house our carbon and GFO. We also run our quarantine tanks with HOB filters. While both forms of filtration will suffice for saltwater inhabitants, we find that sumps provide a greater array of benefits to the saltwater aquarist.

Canister filter originally running on our nano saltwater aquarium.

As previously mentioned, sumps increasing the total water volume for the entire system is a benefit. Sumps also provide a location to house heaters and monitoring probes, keeping them from detracting from the main aquarium’s appearance. In addition, sumps also provide major assistance in regards to nitrate control. Canister filters are typically referred to as “nitrate factories” since they collect all the waste and uneaten food from the aquarium, then house these items within the canister’s chamber until the next filter cleaning. This leaves the waste to collect and eventually break down releasing nitrates back into the water column. Sumps provide a means to empty uneaten food and waste in a more accessible manner. Additionally, they offer the ability to add equipment to further assist with the breakdown of nitrates. We will explore these benefits in greater detail later in the article. Finally, saltwater systems (especially reef tanks) have more water parameters which need to be monitored and kept within acceptable ranges when compared with freshwater systems. Sumps provide an area to attach accessory equipment to help maintain the water chemistry necessary for your aquarium inhabitants. While saltwater aquariums can be run with canister or HOB filters, sumps provide great benefits and efficiency for the overall system.

Basic Design

Now that we have reviewed a few of the perks behind selecting a sump, lets evaluate its construction. The filtration system begins with a means to remove water from the main tank down to the sump with an overflow feature. Many saltwater aquarists choose to go with what is referred to as a pre-drilled tank. This means that the tank has been drilled and potentially plumbed for water to overflow from the top of the main tank. Overflows are typically spotted as a large black column towards the back of the tank. But if large black pillars aren’t your thing, upgrades can be installed on tanks through cutting holes into your aquarium glass and adding overflow kits. These discrete black boxes are positioned towards the rear of the aquarium and are less ostentatious as traditional overflow styles. Reef Savvy offers an extremely sleek looking ghost overflow unit. Or you could simply attach a bulkhead into your drilled holes.

Reef Ready Aquarium with Traditional Pre-Drilled Overflow

However, if you are using a standard aquarium that is not pre-drilled or cannot be drilled (tempered glass should NEVER be drilled as it shatters) this does not mean that sumps are out of your reach. Overflow boxes are sold which rest on the side of your aquarium and allow for skimming water to the sump section. While not the most attractive or appealing overflow option, it does provide a means for individuals to still gain the benefits of using a sump system. We currently utilize this design on our nano reef aquarium.

Once water has left the main aquarium from the overflow, it travels through plumbing down to the star of our article, the sump. Numerous sumps exist on the market by various manufacturers which have been fabricated with standard sump designs. Sumps will usually contain 3 or more chambers strategically situated to assist with water filtration and treatment. Baffles will typically separate these chambers to limit the generation of microbubbles which could make its way to the main tank detracting from the water appearance.

Overflow box resting on the side of our nano saltwater aquarium.

If the prefabricated sumps aren’t meeting your needs or you would like to save a little money (because a penny saved is a penny towards your next aquarium), designing your own sump is always an option. A standard aquarium can be cultivated into a custom sump with a little DIY. This option allows you to construct a design to meet your exact needs. Cut glass siliconed into place can be used to generate baffles for the creation of chambers. However, some choose to forgo sectioning of their sump and have reported minimal issues from microbubbles. We are currently using a previous tank as the sump section for our nano aquarium and have decided to forgo adding baffles. While we might decide to change this option in the future, for now the sump is functioning well without compartmentalization. ​

Test run of sump for nano tank in order to determine best equipment arrangement

When selecting or designing a sump, the main thing to consider is spacial constraints. Make sure to measure the area you have beneath your tank to insure that your sump will fit beneath the aquarium’s stand. Additionally, there is a plethora of equipment you can add to your sump to help improve water quality. We will be discussing some of these options in a moment. You will need to determine the footprint of your equipment to make sure it will fit in the desired sections of your sump.

At the opposite end of the sump from which water initially entered, you will position a return pump to move water back to the main aquarium. When selecting a return pump make sure to review its head pressure capabilities. The return pump needs to be powerful enough to move water against gravity and the distance of your plumbing back to the main tank. Water will then be deposited into your main aquarium through a return jet.

Time to Accessorize!

1.) Filter Socks
Filter socks should be the first item arriving aquarium water contacts when entering the sump. Filter socks can be comprised of either mesh or felt. Their primary purpose is to strain water and extract particulate matter including fish waste and uneaten food. Filter socks are extremely effective at increasing water quality IF they are cleaned or exchanged every 3 days or less. Ignored filter socks will contribute to issues within your tank as the trapped particulate matter begins to degrade and return undesired elements back into the water column. Be honest with yourself, if you can’t truly envision yourself sticking to cleaning the filter sock every 3 days then you might want to forgo this option. Many people choose to run their systems without filter socks. However, for those seeking to maintain the best conditions for their tank or trying to achieve a successful reef tank you need to commit yourself to some sock laundry!

2.) Protein Skimmer
Protein skimmers are arguably one of the greatest advancements within the saltwater aquarium hobby. A protein skimmer is a piece of equipment which removes organic waste from the water column. This is achieved by using air bubbles to remove dissolved organic compounds. The extracted organic matter is accumulated within a collection cup at the top of the device, keeping the waste from breaking down and returning to the water column. The bubbling action emulates waves crashing along shore and the generation of sea foam which is the ocean’s means of eliminating organic waste from our oceans.

Air Bubbles Building in our New Protein Skimmer

3.) Refugium
Think of a refugium as a “mini” aquarium that has been plumped in conjunction with the main aquarium system in order to provide several beneficial opportunities. Sumps offer an ideal location for the incorporation of a refugium. Refugiums can be stocked with additional live rock or Chaeto (Chaetomorpha) algae to provide another means of nutrient export thus aiding in the fight to control algae. Additionally, lighting chaeto algae opposite from the lighting schedule of the main tank will help limit pH swings which occur in aquariums at night. Refugiums can also serve as a ‘refuge’ for you microfauna population. Copepods and phytoplankton can survive and populate within the refugium away from predators in the main tank. This will maintain a steady supply of the little critters for your aquarium system. Some even utilize refugiums as a location to help acclimate new aquarium acquisitions or grow out coral frags.

4.) Storage for Heaters, Chillers & Monitor Probes
Nothing breaks the immersion of your undersea paradise quite like a heater wedged against the side of the wall. Sumps provide a concealable location to place heaters, monitoring probes and chiller equipment. Several prefabricated subs on the market today even include designated slots for securing probes.

Nano Aquarium Looks More Cohesive Without the Distracting Heater

5.) Dosing Systems
In order to maintain proper water chemistry for saltwater aquaria (especially reef tanks) supplemental dosing of elements such as calcium are required. Fortunately, equipment exists on the market to aid in the addition of these paramount elements. Dosing systems traditionally include a holding reservoir for the supplement, pump and tubing. The dosing system can be designed to administer additives directly into the sump water, once again concealing these elements from view.

6.) Media Reactors / Media Bags
It is advisable to run saltwater systems with chemical filtration such as carbon and granular ferric oxide (GFO) in order to improve water quality. Carbon will remove some organic molecules, chlorine, toxins and other pollutants suspended within the water column. Additionally, carbon also removes the substance which can give aquaria water that yellowing tint. GFO will uptake phosphates from the water helping to circumvent algae issues. To see the the chemical media we use within our nano saltwater system, check out our Nano Tank Techs & Specs article. Chemical media can be placed within media bags and placed directly into the sump or housed within media reactors conjoined with the sump. It should be noted that while both options provide chemical filtration for aquaria, media reactors increase the effectiveness of the chemical filtration. Media reactors increase the efficiency by suspending the media granules in order to increase contact with the aquarium water. Media stored within bags tends to clump and limit contact between granules in the center of the bag and the water.

​7.) Auto Top Off System (ATO)
As water evaporates from the tank, the salinity of the aquarium will be altered due to the salt left behind within the remaining water. In order to correct the salinity, saltwater aquaria will need to have RO/DI water added to the system to replace the water lost due to evaporation. An ATO system will monitor the water level within your aquarium and add the displaced water when necessary. The sump provides an ideal location for monitoring equipment to be placed. The ATO water reservoir is typically placed adjacent to the sump.

Smart ATO by AutoAqua utilizes a digital sensor to monitor water levels.

8.) UV Sterilizer
UV sterilizers advertise having the capability to eliminate green floating algae and control potentially harmful microorganism populations within your system. While UV sterilizers do help to clarify green water, there is much debate within the community about its effects on the microfauna populations within the aquarium system. Before installing a UV sterilizer, you will need to conduct research on the pros and cons of the unit to determine if it will provide the benefits you are seeking for your system.

While there are many benefits to relying on a sump for your saltwater aquarium, it should be noted that drawbacks do exist. The addition of a sump will require some forethought in determining the best method to plumb for the system. Flaws within configuration of your plumbing can result in flooding during a power outage. The good news is strategic placement of check valves can prevent this occurrence. Additionally, many report noise level as an issue surrounding sumps. Careful selection of accessory equipment and nozzle placement can dampen the volume of your sump system. We will address methods to prevent these drawback in our next article when we discuss the sump system we recently installed on our nano saltwater aquarium.

So tell us, do you run a sump on your aquarium system? If so, what equipment do you use? Let us know your thoughts in the comments below.

See you next time! Keep Krill'in!