The way I did this was since I couldn't remove my rock drain the tank halfway and a small spray bottle spray the areas but it is still the algae starts to turn kind of a gray color peel it where the allergies dead then refill the tank. For mixing I did half the bottle With water then the then a quarter of what's left peroxide
See I know you can use like 2ml to every gallon and dose the tank but I want to know how long to wait before needing to change the water, also can I do this and do the 72 hour lights out for better results. Last time I wrapped my tank and turned the lights out for 72 hours the hairy algae on the rocks didn't die like everything else
I agree with Randy, i steered away from Peroxide and Lugols and dip my corals with Coral Rx. peroxide seemed a little harsh and i didnt like the fizzyness , Coral Rx still has a potent smell but doesnt react on the corals the way peroxide does. a little better for them IMO. but i am far from an expert on peroxide
Imo peroxide is for algae u cant get rid of any other way like dino's. but if you do dose follow a guide. Also you dont need to change water to get rid of hydrogen peroxide as it is unstable and breaks down easily and almost immediately in your tank. You may however want to water change to keep your water params stable as depending on how much you are dosing you may have a lot of dieoff you need to export.
For best results, remove a rock and put in 50/50 tank water/peroxide. This WILL kill the beneficial bacteria and many coral. However using a spay bottle on a rock outside the tank is my suggestion for most. I like to dip the rock in some water before I put in back in to remove as much dying plant matter. I would not suggest dosing an entire tank as many coral do not take to kindly to that.
As Randy said, it does kill other things. getting your Phos under control and down should come first.