I'm sorry to hear that your boy is going through this. Bladder stones can be difficult to deal with. Testing is done to determine what "type" of stones are present; without this, one cannot get their pet on the correct diet. That said, vet's can often observe what kind they are with relative accuracy. The best prevention for these is a prescription diet. If your dog did not like the one they were one, you may one to try one by Hill's. Another option is to visit a local hoslitic vet or pet nutrtionist. They can advise you on a homemade diet for him. Some owners find that using bottled spring water (or distilled water) can be helpful as well. The following link has a section on making treats from the canned food and also information on another pet owner that was in your situation: http://www.petplace.com/dogs/how-can-i-prevent-recurring-bladder-stones/page1.aspx
I hope he's doing better soon.
It would be advisable to have him into the vet at once if he appears to be in distress. If there is a blockage, even without blood, surgery will likely be needed. The xray will show for sure. I hope he's doing better soon.
Thanks for the update. Medical management is generally the preferred option, more so in older dogs. As he has had these resolve before pre-op, it's likely that this may be the case again. Keeping a close eye (via xray), using the prescription diet (try a few different brands as one may be more to his taste), and utilizing the medication may be enough. You'll want to watch closely for signs of distress, say in contact with your vet and be prepared for surgical intervention if this begins to worsen. As this has been ongoing, you may also want to look into having him seen at your nearest "teaching" vet hopsital (state U etc). They tend to be excellent with ongoing problems and often have specialists on site. I hope he's doing better soon.
Even if the urine PH is not condusive to regular circumstance, they can still form. The distilled water should help prevent future occurances along with the prescription diet. If he is not taking in water at all, you'll want to have him in for an IV. Some owners find that adding a bit of chicken broth (no onions) to the food can help with hydration as well. If he is crying and in pain, even with medication, and continues not to drink then surgery is going to become an option that you may want to think about more. In some pets, theraputic treatments (medication etc) are enough however if they are in severe distress more intensive measures may be needed. Also, if your vet hasn't discussed this yet, ask them if cystitis or interstitial cystitis may be another concern. Some dogs with this can get bladder stones frequently. Consider looking into the state U's (or there affiliates) as these tend to be a great resource. I hope he's doing better soon.