Sump

A sump is an auxiliary tank, typically positioned below the display aquarium, that serves as a multi-chamber filtration system. Water overflows from the main tank into the sump via a weir or overflow box, passes through customisable filtration chambers, and is pumped back up. Sumps offer unparalleled filtration capacity and equipment concealment.

How a Sump Works

1. Overflow: Water exits the display tank through a built-in overflow or hang-on overflow box, flowing down to the sump via gravity.
2. Filtration Chambers: Inside the sump, water passes through multiple baffled chambers containing mechanical filter socks, biological media, chemical media, and/or a refugium.
3. Return Pump: A submersible or external pump pushes filtered water back up to the display tank.

Chamber Layout (Typical)

• Chamber 1: Filter sock or roller mat for mechanical filtration.
• Chamber 2: Biological media (ceramic, lava rock, K1 media).
• Chamber 3: Equipment zone (heater, probes, dosing lines).
• Chamber 4: Return pump chamber with auto top-off float valve.

Why Use a Sump?

• Massive Volume: Adds total system water volume, improving stability.
• Hide Equipment: Heaters, probes, dosing lines, and reactors live in the sump, not the display.
• Unlimited Media: Room for large quantities of biomedia, far exceeding any canister filter.
• Surface Skimming: Overflow inherently skims the water surface, removing protein film.
• Customisable: Each chamber can be tailored to your specific needs.

Sump vs. Canister Filter

Key Considerations

• Overflow Method: Built-in overflows are safest. Hang-on overflow boxes work but carry a slight siphon-break risk.
• Return Pump: Size the pump to deliver 5–10x tank turnover after accounting for head pressure (the height the pump must push water).
• Noise: Overflow plumbing can create gurgling. Durso standpipes or Herbie drains significantly reduce noise.
• Flood Prevention: Always test your sump's capacity to hold all drain-back water if the return pump fails.

Pros & Cons

Advantages

• Filtration Capacity: The most powerful filtration option available.
• Hidden Equipment: Clean display tank.
• Water Volume: Increases total system volume for parameter stability.
• Flexibility: Fully customisable chambers.

Considerations

• Cost: Tank, plumbing, pump, and overflow add up.
• Complexity: Requires plumbing knowledge and careful setup.
• Space: Needs a stand or cabinet large enough to house the sump.
• Noise: Must be properly tuned to avoid gurgling.