When we got our first dishwasher (Bosch) I used to put salt tablets in, partly because you couldn't set a zero-level for hardness and a friend of mine had been told by a salesman that the salt helped with the germ-killing in the wash. I used the same tablets as our Culligan water softener ie, fairly large ones. When we replaced it about 15 years ago (another Bosch) we were able to set it for zero-hardness and I stopped using salt altogether. I think the germ-killing bit was a load of rubbish and soft water in a dishwasher is solely to make sure the jets don't clog up with scale, which would seriously affect the cleaning.