overflow box

Noteworthy Points:

Green Light: Return pump ON

Water rises to tank

Return area lowers

Display fills higher

Overflow fills

Overflow drains to sump

Sump fills

Red Light: Return pump OFF

Residual water in plumbing drains
    down

Drilled hole in return line
    breaks siphon

Water in sump and refugium
    rises

Siphon is maintained in
    the overflow box

Sump is tall enough to hold
    excess water

A sump gives you greater control over your reef or fish-only display tank. The benefits far exceed the risks, and thus most successful aquariums you'll see utilize a sump. Some even incorporate a refugium as well. Here are the numerous benefits derived from incorporating a sump into your current setup:

• Increased total water volume - This dilutes your water of accumulating pollutants, and helps avoid issues that occur quickly in sumpless tanks.
• Skims the surface - No more surface scum, just crystal clear water.
• Lowers temperature - I've observed a 2° F drop after the sump is installed.
• Hides equipment - Heaters, protein skimmers, monitoring probes, grounding probes and more can be moved to the sump & out of the display tank.
• Consistent water level - The display tank will maintain the same water level all the times; evaporation occurs in the sump over time (see auto top-off).
• Safe place to pour in additives - Adding chemicals or new (Reverse Osmosis De-Ionized) water in the sump allows it to mix before entering the display tank.
• Increased circulation - The return water from the sump is yet another way to move water in your tank. You can point the return outlet(s) in different directions to create flow, instead of putting more powerheads in your display tank!
• Increased oxygenation - As water drains into your sump, air mixes in the water, allowing beneficial gas exchange, releasing CO₂ and adding fresh O₂.