Aesthetics

• Sumps can be designed to keep water in the display tank at the same level, while the sump level lowers and raises with evaporation and water additions. Equipment such as filters and skimmers also can be installed in the sump instead of the main tank.
  
  

Aeration

• Proper aeration is critical for aquarium health. Water flowing over the overflow and back into the sump creates aeration.
  
  

Increasing Water Volume

• The greater the water volume in an aquarium system, the more stable the system. A sump adds water volume to your aquarium system without increasing the size of the aquarium.
  
  

Reducing Surface Contaminants

• The overflow mechanism of a sump naturally pulls the top level of water into the overflow. This means that the surface of the water is constantly being skimmed.
  
  

Maintenance

• You can top off water and add medicine and additives to the sump instead of to the main tank. The sump is typically easier to access and putting additives in the sump allows them to mix with the existing water before going into the display tank.