Aerangis modesta black dots on leaves
 

I've only had my Aerangis modesta for a few weeks and shortly after bringing it home I discovered black dots on the lowest leaf. The leaf eventually shriveled a bit and died. Then the next leaf up got black dots and died. Now almost all the remaining leaves have black dots (about 1/2 cm in diameter and round). I tried spraying it with Listerine because I thought it was fungal. It just seems to continue spreading. Growing conditions are low light, 40-70% humidity and I've been misting it every second day or so (trying not to hit the leaves, but the roots are all over the place). What else could it be?

I get similar dots on my Aerangis citrata, it seems to happen when it is cool, damp, and little air movement.