Hey Mustang,
How much 3% H2O2 you should use add depends on how often you want to add it.
If you want to add H2O2 on a daily basis then 5ml per gallon = 35ml of 3% H2O2 for your res daily would be a good amount.
If you want to add it say 3 times a week then use 10ml per gallon = 70ml of 3%...