When I read your letter, I must admit I have never heard of this "home remedy". From my experience, alka-seltzer would not cure bladder/urinary tract infections. The only cure I
know of for a urinary tract infection (UTI) is antibiotic therapy.
Alka seltzer is mainly made up of aspirin and citric acid, both of which are not a treatment for UTI. Since it is a pain reliever, this may take the burning on urination pain away, making someone think that their infection is gone. I would caution you that just because you don't have burning doesn't mean you are "cured". The only safe way to know if you don't have a UTI is to get your urine tested and have it come back clean.
A word about citric acid: we know that urinary tract bacteria do not like acidic urine. This is why cranberry juice and vitamin C can be helpful for preventing UTI's in some people. But again, these are not cures!