you can but your gonna need to use alot of it. When i was growing in hydro i just bought the 30% h202 from the grow shop cost like 16 bucks but you only gotta use like 5ml per gallon. So u can use the 3% but your gonna spend alot of cash buying enough to sustain your grow threw the whole cycle.
I will add directly on top of Rockwool for surface cleanse.I dilute 5-10 capfulls to a gal of ph'ed water for a root cleanse.I will use a stronger dilution if problem in root zone is more serious.I use it as a general maintenance tool,and not so much for Oxygen for roots.
I will use regular bleach seperately at 1-2 DROPS per gal in my nute solution or DWC cloner every 3-4 days for maintenence.
Peroxide should work with all synthetic nutes,I reckon.