Re: ID of the creepy powder on my hive's inner cover?
I suspect most of mildew/mold is on top side of inner cover. Bees give a lot of moisture metabolizing carbohydrates over winter. It is around 5 gallons. Your moisture problem is further compounded by feeding syrup. Bees are storing it and drying it down.
Trust inner cover has center 2 plus diameter center hole. You need to better vent top area of top side on inner cover and under side of outer cover.
1. Place a spacer such as pennies or popsicle stick width on top side of cornesr of inner cover. This slightly raises outer cover and provides a gap for venting of top side of inner cover.
2. Have the notch in rim of inner cover facing up. Air will rise through center hole of inner cover and vent out notch.
3. Use a quilt box above inner cover. I have a 3/8 rim on under side of inner cover and this is how I run my hives.
4. Remove inner cover and use a quilt box.
5. Place a piece of Styrofoam under or on top of outer cover to keep warmer and minimize condensation.
Zone 3b. If you always do what you always did, you'll always get what you always got!