I bought some Mason jars today with the correct metal lids. Metal lids with plastic or non metal interiors inside the lid. I put together a few batches of the water kefir with lids on tight hours ago and haven't had any problems.
I went to YouTube and the videos that I watched all said not to put the lid on tight and really said no lid at all. Weird I know. I just didn't want to have to get more grains. I liked the way mine were growing.
I hope this works, I really need the Kefir water to be right.