After softening hard water, what will be the TDS of this treated water?

Hi 

When we had tested the raw borewell water it showed a TDS of 870 and hardness of 490. After treating it using a softener we expected that the TDS would come down to 400 and hardness would be nil but we are getting a result of 120 TDS. Is this possible? 

Also please tell us how to recalliberate our TDS meter?

 

 

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