Sump Filter: A Guide
A sump is a secondary tank below the display aquarium that hides equipment, adds water volume, and improves system stability.
Overview
A sump is a secondary aquarium, usually placed below the display tank, that holds mechanical equipment out of sight. Water flows from the display by gravity into the sump, passes through filtration compartments, and is returned to the display by a pump. Sumps are most common in reef and marine aquariums but are also used in large freshwater systems.
How it works
Water leaves the display tank through an overflow and descends into the sump under gravity. Inside the sump it can pass over a drip plate and cascade through several media and equipment chambers before collecting in a return section. A return pump then sends the water back up to the display, closing the loop.
What it houses
- Protein skimmer
- Heater and thermostat
- Mechanical, biological and chemical filter media
- Calcium reactor or other dosing equipment
- Optional refugium compartment
Benefits
The added water held in the sump increases total system volume, which buffers fluctuations in pH and salinity and makes the system more stable. Moving equipment into the sump leaves the display tank clutter-free. Water movement between the sump and display improves gas exchange and raises dissolved oxygen. A refugium section can be added to help remove excess nutrients such as nitrate.
Limitations
A sump requires space beneath the aquarium and an overflow plus a return pump, which adds plumbing complexity. The exposed water surface increases evaporation, and a failure of the overflow or pump can cause flooding or running dry. Setup and maintenance are more demanding than for a self-contained filter.
Maintenance
Mechanical media and any filter socks should be cleaned or replaced regularly to prevent trapped detritus from breaking down. Skimmer collection cups and pump intakes are checked on the same schedule. Evaporated water is replaced with fresh water (or top-off) to keep salinity stable.