Giardia but vet says don't treat it. Please help me out.

This is going to be long and I apologise in advance but please read and help me out. We are on our second vet now and I just don't know what to do.
It all started back towards the beginning of June. My 4 month old chinchilla stopped pooping. He also wasn't eating much and was barely touching water. He went to the vet and they prescribed critical care. He had to be hand fed the CC and really wasn't enjoying the whole process after about a week I called the vet to give him and update and...

Giardia but vet says don't treat it. Please help me out.