I use 3% BRS has a video from MACNA which gives you all the detail and ratios of peroxide to water you should use for a given coral I kinda eyeball it using the cap and stuff but definitely give it a watch if you want to do it the right way!! Some corals tolerate it better than others, and if it takes a while for the coral to open up its normal its because peroxide is very harsh on them
I pour enough 3% in a cup to cover the frag and drop the zoa's straight into it. Let it sit for about 1 1/2 minutes, rinse it in some tank water then back in the tank it goes.