He was and is acting completely normal. I noticed the blood on his pee pads. He hasn't been having difficulty urinating so far, so I hope it stays like that. The vet ran the tests and took an xray - it shows that there is just "powder" in his kidneys, so they haven't formed into stones yet
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He's now on prescription dog food for the next month. We gave it to him mixed in with his usual kibble and he wasn't thrilled about it, but ate it after much coaxing.