I think its Powdery Mildew

I believe it is white powdery mildew, its easily wiped away and started on my clay pebbles, now its spreading to rockwool. What are my options to fix this and is it a serious major immediate threat to my plants? Please respond and I would really like to try to solve this with a home remedy because my hydro shop is far very far.

Thanks everyone!

And also I started adding hydrogen peroxide to help with oxegenation, root rot, and over feeding issues. can this also be helpful to help prevent and cure this mildew and other issues that may occur?

the plants don't have enough ventalation and air circulation this causes mildew.