Many 1/8" chains are pressed together, not 'quick-linked'. But adding links to a chain is one of the easiest 'fixes' there is. All you have to do is make sure the chain is snug before you get to the back of the diagonal dropouts. In fact, one of the little tricks I use is to snug the wheel all the way back in those dropouts, and then size the chain like you would for a multi-speed -- wrap it around each gear, front and back, see where they come together, and remove one more link.