Peroxide ???

I have used a solution of a capful to a small (6 ounce) spray bottle to kill gnats by spraying the dirt. Some of it got on the lower leaves and I didn't wash it off or anything. It looks fine. But I wasn't spraying the foliage on purpose. Hope this helps.

Why do you want to spray it on the leaves?

Wanna fight mold and fungus i saw where fdd uses it but i didnt catch the details

thought thats just to add extra molecule when watering heavy so the roots get oxygen........... im new to this tho so i could b wrong

Don't. For mold/fungus use a sulfur vaporizer.

Or just beat the whole cycle and keep temps and humidity in check.