Your vet is really the only person who can confirm the dosage.
I know it is used to acidify urine in cats and dogs, but haven't heard of it being used in guinea pigs.
I do believe that the general consensus is that urinary acidifiers aren't overly successful in guinea pigs.
Can you give us some more details on how Coco's problem was diagnosed - urine sales, x-ray, ultrasound, etc.
It would help a lot of you could at least provide us with your country or state, so we can offer more targeted and relevant information as medications are often different in different places.