I would go with a Clack WS1 or Fleck 2510. The greensand media is heavy and requires higher flow rates to properly backwash. With the 2510 the max backwash flow rate is 17GPM and the WS1 is 27GPM. I sent you a PM.
Try this company I purchased one its a steal. Few other people I know use him.
$399 softened our in 3 days. Install took me two hours.