I don't think your grains are ruined, but they might need a rest. My grains started acting funky, the finished kefir started smelling/tasting like sulfur. There was also other things just "off" about it. They also weren't multiplying AT ALL, and actually started breaking down.
To be fair to my grains, I had been pretty abusive to them, keeping them in the fridge for about two months without feeding, not brewing on a consistent schedule, using a metal strainer, etc. I'm working on rehabilitating my grains right now, I put them to rest last night. Maybe you could try a rest with your grains and see if that helps. Cultures for Health has a great article on how to rehabilitate your grains. Best of luck!