It's two different processes.
Rock that has been in high phos conditions, like underground with water passing through it from the surface, or a dirty tank, will store it up. Then when it gets in a low phos condition it will release it. If that happens in your tank, and everything else algae needs (light, nitrates etc) is present, algae will grow. So people put it in a low phos enviro with something else missing, usually light, so that the phos will be released but algae won't be able to use it to grow. That's what people are doing with brutes and phos removers like gfo reactors or lanthanum chloride. Marco is claiming they took care of that part for you already.
The other process is growing the bacteria on the rock. This "cure" is just a head start on the cycle.
I like to do both right in the tank before I turn on the lights, without a sand bed. As the rock cycles and releases phos a lot of detritus is produced. It's dead bacteria and other crud that accumulates as the bac get their population balanced and pull stuff out of the rock. If you wait until that part slows down, you can easily remove that detritus from the system. If your rock turns out to be phosy, you can easily run LC to remove it. Then once the rocks are all cleaned out and the bacteria is processing ammonia, I add sand and turn on the lights for a week or so before I start stocking.
I agree with the poster who said phos leaching is a boogeyman (except for Pukani rock, that stuff is a nightmare). I think most of the time people run dirty tanks but don't realize because the rock is soaking up the phos, then it gets "full" and stops. If it's in there from the beginning, you'll know within a week because the phos-less water it's in will start to test positive. For that reason I do wait a week before I start feeding the tank to grow cycling bacteria, since the added phos from food would mess up the test. I guess if you use ammonia that's not an issue?
