← Glossary · ⚙️ Equipment & gear
Sump
A sump is a second tank plumbed below the display that adds water volume and hides equipment — skimmer, heater, return pump and often a refugium — out of sight.
More water volume means more stability, which is why sumps are popular; but plenty of successful reefs, especially nanos, run without one. Count only the actual water in the sump toward your system volume when dosing.