Kat --
I had a female ferret years ago who not only developed the crystals, but
got full-blown bladder stones.  While antibiotics (and I think Baytril is
what's usually used in this case) will help with any possible infection,
your primary problem still remains -- Uh-Oh has the tendency to develop
crystals in his urine.
 
Chances are you will have to make some dietary changes in order to prevent
the crystal growth.  In some cases medication may be necessary.  My
Claudia had cystine bladder stones (most ferrets and cats get struvite) so
she went on experimental medicine that kept her alive for another 6 years.
 
It's important to find someone who has some knowledge with this -- I had
a vet who kept telling me Claudia had bladder infections, or UTIs, when
she could have died if one of those stones had ruptured her bladder.
 
Good luck!
Amy, Dave, Sarah & Paul (and their gaggle of giggling ferrets)
RIP Ian, Elektra, Claudia & Sidney
[Posted in FML issue 3841]