Like the lady said. Use 3% food grade.
U can use up to 2 1/2 tsp per gal. But as said, start low.
I use it if I developed a problem, other wise, I don't use it on a regular basis.
Usually if ur talking hydro , the remedy to any of the problems U would have where ya need H2O2 , would be to add more air.(with DWC)
If my penis is 12" long. Is it a Foot?