Well thank you for that.
I've been hanging around just getting a feel for the place, and see that the excellent veterinarians here offer occasional guidance but mostly lay low so as not to put a 'chill' on discussion, an approach which I wholeheartedly endorse.
My point on the oxalates was that its fine to use cranberry or vitamin C to 'promote urinary health' and such, but if your dog has straining, blood etc. of course get it checked out, but also make sure the veterinarian knows you are using the acidifier.
In general the dog with straining and blood in the urine runs about 90% infection, 10% stones and crystals, and less than 1% tumors, but in the older dog always a thought. Ways to look for stones include palpation, urinalysis, X-rays and sometimes ultrasound. - Dr. Mac