capel dishwasher Di 604?

My capel dishwasher which I have had for approx 15 months is releasing all the salt from the dispenser in one go, leaving all the plates, glasses etc covered in a white film. It worked correctly when we first had it. We have tried adjusting the black arrow (plus and minus signs) in the salt dispenser unit, but it makes no difference. It is only over the last couple of months that it has gone wrong. Without any salt in the dispenser, the finished results are OK, but will it do any harm to machine if salt is omitted, as we live in a hard water area. (The dishwaster tablets used have a small amount of salt in them anyway)