The issue i suspect you're having is one of sugar bloom, and that results from condensation. You get condensation when something cold runs into warm air (warm air contains more water than cold air) - and when the warm, wet air hits the cold chocolate, that decrease in air temperature means the air can't hold the excess moisture, and it promptly deposits itself on your bar. When it does so, it dissolves some sugar in your chocolate, and then it eventually evaporates and leaves behind the dissolved sugar that looks now like white film.
Your typical consumer fridges have thermostats that aren' meant to go as high as 55 - some models have a cowling that, if you remove the cover, there's a set screw that you can turn to further adjust the range of the condensing unit to enable it to achieve warmer temperatures - its a trial and error thing as there's no gradations on the set screw (and not all modesl have it) - you just have to turn it, put a thermometer in there and read it 4 hours later to see what's happened. If yours has the set screw, it's the least expensive way to modify your fridge. If not, you can replace the thermostat - it's not hard to do, but not everyone's comfortable cutting wires.
A very helpful tool for managing condensation is a psychrometric chart - big scary word, the chart itself is also scary looking, but once you understand how to read it, will help you understand what the temperatures of your fridge (or the room your fridge is in) need to be to minimize the odds of condensation.