Last Updated: June 8, 2026
Introduction
A sump is a secondary tank placed beneath your main display aquarium that dramatically increases total water volume, provides a hidden space for equipment, and allows far more flexible and powerful filtration than any hang-on-back or canister filter can offer. Sumps are standard equipment in reef aquariums and large freshwater setups, and understanding how to design and set one up correctly is a key skill for advancing hobbyists. This guide covers the essential components and best products for a functional sump system.
What to Look For
- Sump sizing: Your sump should hold at least 20–30% of your display tank's volume, though larger is always better for increased water stability and equipment space. Account for flood-back volume — how much water drains from the display if the return pump fails — when sizing the sump to prevent overflow.
- Filtration compartments: An effective sump design includes a mechanical filtration section (filter sock or filter roller), a refugium section (for macroalgae or live rock in reef systems), and a return pump section. This compartmentalization maximizes biological filtration and water processing efficiency.
- Return pump selection: The return pump drives water from the sump back to the display tank. Choose a pump with adjustable flow rated at 4–6 times your display tank volume per hour to compensate for head loss from the vertical plumbing run.
Top Picks
Trigger Systems Ruby 30 Sump
The Trigger Systems Ruby 30 is a purpose-built acrylic sump for reef aquariums that offers an intelligently designed layout with an integrated filter sock section, refugium compartment, and return pump bay. Its high-quality construction, clear acrylic panels for excellent visibility, and thoughtful chamber sizing make it a top choice for 75–150 gallon display tanks. Trigger Systems sumps are consistently rated among the best in the reef-keeping community.
Mag-Drive Supreme 7 Return Pump
The Supreme Mag-Drive 7 is a reliable, energy-efficient return pump rated at 700 GPH that suits sumps on display tanks from 55 to 125 gallons. Its magnetic drive design is safe for use in reef aquariums (no oil-contamination risk), operates quietly, and is easy to disassemble for cleaning. Adjustable output via a ball valve on the return line allows fine-tuning of flow rate to match your specific plumbing configuration.
Filter Sock 7-Inch Ring Aquarium Filter Bag
Filter socks are the first line of mechanical filtration in a sump, capturing particulate waste before it can decompose and leach nutrients. A 200-micron filter sock removes suspended debris effectively without restricting flow, and having multiple filter socks allows rotation — one in use while the other is being cleaned. Replace or rinse filter socks every 2–3 days to prevent trapped waste from becoming a nitrate factory within your filtration system.
How a Sump Works and Why Aquarists Use One
A sump is a secondary tank, usually placed in the cabinet below the main aquarium, that increases total water volume and hides equipment out of sight. Water flows from the display down to the sump through an overflow, passes through filtration and equipment chambers, and is pumped back up by a return pump. This added volume improves stability, since a larger total water mass dilutes waste and resists rapid swings in temperature and chemistry. Sumps are especially popular in reef and large freshwater systems where equipment and water quality demands are high.
The biggest advantage of a sump is flexibility. It provides space to house heaters, protein skimmers, media reactors, and dosing equipment outside the main tank, keeping the display clean and uncluttered. A sump also creates a stable, hidden spot to top off evaporated water and run an auto top-off system. Sumps are typically divided into chambers by baffles that direct flow, often including a section for mechanical filtration, a refugium for beneficial macroalgae or live rock, and a return chamber where the pump sits.
Designing and Running a Reliable Sump
Proper sizing and flow are key to a trouble-free sump. The return pump should match the overflow’s drainage capacity and your tank’s needs, providing good turnover without overwhelming the overflow. Crucially, you must account for backflow during a power outage: when the pump stops, water siphons back into the sump, so the sump must have enough empty headroom to hold that drained water without overflowing. Marking your normal water line and testing a simulated power-off before adding livestock prevents floods.
Filter socks or sponges in the first chamber catch debris and should be cleaned or replaced regularly to prevent clogging and detritus buildup. Plumbing should use proper unions and aquarium-safe fittings so equipment can be serviced easily, and a check valve or a properly drilled return line helps manage siphon. Keep the return pump and skimmer chambers at consistent levels, since fluctuating water height affects skimmer performance and can introduce noise. A well-designed sump, set up with attention to flow and backflow safety, transforms an aquarium into a more stable, capable, and easily maintained system.
Frequently Asked Questions
What is the point of an aquarium sump?
A sump adds water volume for greater stability and houses equipment like heaters and skimmers out of sight. It keeps the main display clean while improving filtration and water quality.
What size sump do I need?
Choose the largest sump that fits your cabinet, since more volume means more stability and equipment space. It must also have enough empty headroom to safely hold backflow during a power outage.
What happens to a sump during a power outage?
When the return pump stops, water siphons back down into the sump until the levels equalize. The sump must have room to hold this drained water, so always test for backflow before adding livestock.
How do I size the return pump for a sump?
The return pump should match your overflow’s drainage capacity and provide good turnover without overwhelming it. Accounting for head height, the vertical distance water is pumped, is important since it reduces a pump’s effective flow.
What is a refugium in a sump?
A refugium is a sump chamber housing macroalgae or live rock that helps export nutrients and provides a safe zone for beneficial microfauna. It naturally improves water quality, especially in reef systems.
Final Thoughts
A well-designed sump transforms your aquarium system from a single-display-tank setup into a robust, professional-grade filtration platform capable of supporting demanding fish and coral loads with consistency. Plan your sump layout carefully before purchasing components, size it generously, and ensure your return pump provides adequate turnover for your display volume. The initial investment in a proper sump setup pays for itself in reduced maintenance, improved water quality, and significantly greater aquarium success.
