As an early bday present, the gf got me (or allowed me to get, more accurately) a used Melev's Reef RO unit.
http://www.melevsreef.com/rodi.html
Came with connections to set it up to the washing room, a refractometer, a TDS meter, 2 35 gallon water holding bins, 2 K3 powerheads for mixing, 1...