Renal LP for Struvite Crystals?

Hey guys, 

The boyfriend went out to get more cat food, usually Urinary SO, but came back with Renal LP. The vet had run out of Urinary SO and had told him the "kidney food", Renal LP, was the "next best thing".

I understand that the dietary maintenance food for Struvite crystals includes Urinary SO because it makes the urine more acidic and less alkaline, but the Renal LP is for Urate crystals, which forms in acidic urine.

Does this mean that the Renal food will make his urine more alkaline? Is it going to be okay to temporarily feed him the Renal food?

We're going to get the right food ASAP for sure, but I'd like to understand how the different foods work and how it will affect his little cat body in case this ever happens again, as well as for my general knowledge.

Thanks in advance 

Is it the dry or the canned. It should be fine as they are designed to keep the urine ph at the correct level so not to acidic or to alkaline. Although any change in food can cause GI upset.

You might want to check in at the nutrition section of this site for more info as I don't really have as much knowledge on nutrition as I really should.