/diy/ - Do It Yourself

Anyone have any idea of what this purple stuff is? Showed up before when I put together some sanitizer to bottle some stuff. Figured it just needed to be cleaned and used a different bucket. Going to whip up a batch of cider and lo and behold it shows up again even after a cleaning. It rubs of pretty easy, but is there anything I need to be worried about before putting my cider in? Trying not to dump $30 down the drain.