Bleach soak first. It dissolves all the dead organics off the rocks in order to allow the acid to dissolve the top layer of cruddy rock off. Plus, the acid breaks down the residual bleach so that it will off gas as chlorine gas. That sounds bad cause its toxic, but if you do it outside the small amount of fumes won't hurt. Just don't stick your head in the container you're doing it in.
I used the 33 gallon brutes. Put rock in it to the tab (4" from the top). Then filled half way up with water (about 10 gallons). Dropped two gallons of bleach, then added enough water to cover up the rock. Let it sit over night. Drained it off. Sprayed them with water hose to get all the loose stuff off. Then did the same with the Muriatic acid. After about 10 minutes it stopped bubbling once the acid was all used up. I drained it off, sprayed them down. Put a few boxes of baking soda in a 5 gallon bucket, then dunked each rock. The baking soda probably was a little overkill, but I figured what the heck. I'm already doing it and it was a few bucks.