Sounds like a water softner issue. Firstly, ring your local water company and ask them about your water. Is it hard or soft or medium? They should also tell you the figure, (Clarke Scale)of how hard or soft the water is. Then depending on the answer adjust your salt dispenser. Lower the number, for soft water, (1 or 2) higher number,for hard water (3 or 4) Also check your rinse aid dispenser & adjust that figure. Try 2 or even a 3 - It is a case of trial and error but you get there in the end.
Even with these 3 in 1 tablets, still use a separate salt, rinse aid. Your water softner unit in the machine needs the salt in order to work correctly. Failure to use it, can result in premature failure of the machine. http://www.ukwhitegoods.co.uk/index.php is a brilliant site that can answer all things techy with domestic appliances & http://www.dishwasher-care.org.uk/ is very good if you get stuck & need advice as well.
Good Luck.
Alison Graham
July 2007