crystals in urine

Hi my dog was diagnosed with a bladder tumor in sept 08. we had the tumor removed in october 08.We were advised that chemotherapy would not be an option in our case and decided to go for quality of life rather than quantity. Our dog has to have regular urine tests which until last week had all been clear.However we have now been told that he  has crystals in his urine.      Has any one else had this problem with their dog. My main concern is that he takes a lot of medication already . Also i worry that maybe now we are on a slippery slope.Intially we were given a life expectancy of a couple of months for him. We are already beyond that. I would be grateful for any advice.           Thankyou