does water softener bring my ppm down to 0?

I recently rebuild a 10+ year old water softener in the house we just bought. After doing a couple rinse cycle with some rescare, cleaning out the brine tank, and added new salt. My water hardness went from maybe 500-600 down to around 40. Is that good enough or should I be getting a reading of 0? I'm using this to test my water Robot Check (http://www.amazon.com/gp/product/B00DIJ0W30/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1)