The bio spira does not go bad just because the package is opened. I would close it up if I could though just because the air might dry it up like it would anything else in your fridge not wrapped up. You don't have to use it all at once, and 6 months is how long it's recommended to keep it. I have some in my fridge 8 months old and wouldn't hesitate to use it. The bacteria is kept dormant by refrigeration, and probably starts to die off after the 6 month mark. I would not throw it away!