I'd recommend a light spraying with Serenade. It has worked wonders for me. It's a bacteria that eats mold and mildew, then dies off. It's smells a little weird when you spray, but the smell is gone in a few days. Personally, I'd be nervous about spraying with other things, because moisture on the buds might bring on mold/bud rot. If you're not seeing mildew on your buds, then I'd try to mainly spray leaves, and keep any spray on the buds very light (though it should be safe anyway, since the bacteria eats mold/bud rot too).
Also, like Cali said, try to get the humidity down as much as you can.
And, in the future, spraying with Serenade a little after you switch to 12/12 (a couple of weeks in) should stop this problem from happening again.