We've had the dishwasher for 6 years - haven't changed the type (or very small quanity) of soap used; but in the past month or so, the dishes are increasingly NOT getting clean. They are cloudy and sometimes residue is left on them (not food, but powder). Repair person has been out twice and no one can figure out what's wrong. Any suggestions would be helpful. Can I try using a liquid soap? the Technician tells me no, but coworkers say that works great....Please Advise with any suggestions.