Cat Urolithiasis

hello,

my cat (male, 3.5 years old) had urethra blockage twice before (in a 1.5
year period) due to struvite crystal formation in his bladder
he has been on a specific diet (hills c/d) which is a low-magnesium
acidifying food in order for the crystals to be dissolved. he was also fed
another acidifying medicine (named methygel)

yesterday he had another blockage, i took him to the vet and he has been
catheterized. the vet took urine samples and measured the pH which was
very acidic (6) and checked them at the microscope but couldnt definitely
determine if the crystals were sturvite or calcium ocalate. one logical
explanation is that the acidifying diet aimed at struvite crystals made
way for the formation calcium oxalate ones. but the clues tend to
sturvite..

my questions a
1. is it possible for sturvite to be formed in such an acidic environment
(pH = 6)?
(though today, after being fed a normal food, the pH was 8.5!)

2. how easy is it to determine wether it's struvite or calcium oxalate? in
the microscope there can be seen a variety of shapes and forms of crystals
(but not a great number of them). is there another more accurate method?


any help would be valuable
thank you