Hi there,
To acidify the urine, Hydrangea and Eupatorium should work (NPHC).
Regarding the recipe they are using, if it has a lot of starches in it (potatoes, rice, corn, etc.), it will still be problematic. It needs to be more 'paleo', based on meat and vegetables. About as starchy as you can get is sweet potatoes. If you have the Manual of Natural Veterinary Medicine, you can find the basic outline of a paleo diet (from Susan Wynn) in the appendix on diets. I cut back on the oil and salt a bit, but otherwise use it as the home cooked diet template.
Lastly, some more details on his skin, pulses and tongue might be helpful. Here are some recommendations for an additional formula to treat the skin:
If he has a weak pulse with dorsal skin lesions primarily, then Chu Shi Wei Ling Tang (Kan's Dispel Dampness and Nourish the Skin) is a good idea. It has some Ze Xie in it to help hinder calcium oxalate crystals.
If his inflammation is more fulminant and his pulses are stronger, then look at Si Miao San
If he has been consistently on a low carb meat-based diet with no carb or kibble snacks at all, and his skin is no better at all, then we might need to look at Xiao Chai Hu Tang + Si Wu Tang for his skin
If there is the possibility of a low grade recurrent bacterial cystitis here, and his skin is a little better, then you could look at Bu Zhong Yi Qi Tang
Hopefully this helps you out!
Steve