powdery mildew on vegging rockwool cubes

Hey everyone, I had some issues in my room involving a family member coming to stay and trying to keep a low profile, long story short my exhausting fan was off for a couple days and my humidity jumped to 90% in that time frame. Now im hit with the problem of powder mildew. The mildew is only on the Rockwool, not visible on the plants that I can see. Any recommendations for removing it? I've read about milk solutions, baking soda solutions, and hydrogen peroxide formulas. The guy at my local hydro store recommened draining my res and filling it with just water and h202, he said to flush a few times for a day, then spray on this safer brand 3 in 1 garden spray for organic gardening that kills mites, controls fungus, and kills insects. If I try to flush my cubes, they are on rockwool blocks for the roots to grow into and the tops of the cubes won't be covered in water when the tray is full. Does this mean I should make a h202 concentration to pour on the top of the cubes to directly treat the problem, or will the blocks absorb the h202 solution from the bottom and that would be sufficient. any help is greatly appreciated, I don't want to lose my first gro haha but if it has to be done then it has to be done

02 burner is best bet.

an o2 burner? is that like a torch? i picked up some sarenade disease control to use instead of the 3 in 1 garden spray any other feedback?

Google o2 burner.