Thanks for that info, yes i am concerned about her maybe forming the other crystals too, although it is not meant to happen very often, obviously it does and can, i fed her some last night and she ate it no problem, however was only like five biscuits, today i mixed them in with her old ones and yes you guessed it, the new ones were the only ones she left, so i am thinking she is not too fussed, i only went with hills because they sell a bigger bag and money back guarantee,but if royal canin stop both crystals forming, sure sounds a better option to me, might have to re-think this situation.