I've used 10 ml a day through a baby syringe(not sure what it is called but you use it for cough medicine). 1ml a gallon shouldn't harm livestock, but I've heard people doing 5ml a gal. my plants and fish are fine 1 angel baby, 2 Gbr juries, and a baby betta.
What I would recommend is taking out the Marimo ball though since it is an algae and will get affected with h2o2. I'm not entirely sure on the anacharis though, but I remember it gets affected with excel. Turn off filters and lights while spot treating and I also add a power head after dosing so it can circulate the h202 more. If you don't have a powerhead it's okay also. Do water changes, a day after then repeat if necessary.