The water in my dishwasher is not draining. It goes through the cycles but there is always water at the bottom that is not draining. I had a handyman come and drain from the bottom and it was ok for a day then started again. He thought it was from hard water build up because when he drained it from the bottom it was like little rocks coming out. My question is what can I put in there to disolve the calcium that is building up?