Probe Density

The Aquatronica high conductivity electrode connects to the
  power unit with the dedicated interface, so as to measure the conductivity
  (density) value in continuous immersion in the seawater aquarium. This value
  can be viewed as conductivity, density, specific gravity and salinity. The
  flexibility of the Aquatronica control systems also allows multiple
  electrodes and interfaces to be connected and monitored simultaneously to the
  same system.