Dry rock cycle

[SmallFry]

The rock I ordered from you arrived, and I have to say it's amazing stuff, light, porous, interesting shapes - I wish I'd been able to start out with this stuff instead of that unpleasant DIY rock that I'm replacing.
Shipping was fast too - ordered on Saturday night, here Wednesday.
While I was messing around working out how to aquascape it, a desicated and very dead little red crab fell out - that's how you know it's the real thing!

It set me wondering what sort of a cycle you typically get from this stuff - are there a lot of organics in it to decay, or is it pretty clean? I ask because it's replacing all the rock in my display, and I want to be sure I have enough older rock in my sump to deal with any extra temporary bio load from the rock as well as that from the current inhabitants.

Thanks,
Rob.