DOS Dosing and Fluid Metering System - Neptune SystemsDOS Dosing and Fluid Metering System The Neptune DOS Fluid Metering System is one of the smartest dosing pumps on the market. It will hook directly to your existing Neptune Apex, ApexEL or Apex Jr. giving you the ability to program both pumps independently for what ever kind of dosing your tank may need. The DOS pump includes two pump heads for the most common of two part dosing, but it is not limited to just two part dosing. You can use it for