I've also kept them a week without any problems. But when the water temp is high like it is now, I think they get stressed going from hot to cold fridge or ice. I've had batches with a few that would open open a sliver. Part of the tongue would be sticking out. I'd tap it and it would usually close. If not I tossed it. My clams from a week ago were fine, but my nephew had some opening within a couple of days after a 40 minute ride home with them on ice.