KregRS

A friend has got a C4 grand picasso, has been having a few problems with it. The main dealer have said it is low on additive, blue liquid, for emmissions.
Would this be the same as Adblue? And would sticking some Adblue in cause any problems, or would it have to be the stuff Citroen are pushing them to use. The reason for asking is the price, Adblue is a lot cheaper than Citroens brand of additive.
Cheers,