Base rock to live rock

I currently have a 90 gallon fowler tank that's been setup and running for over a year now. Anyway I've been getting bored since I can't add anything else to it so I've decided to setup a 20 gallon nano tank and eventually give corals a try. I have a bunch of base rock from marcorock that I never used so that's what I'm going to use in the new tank.

My question is how long will it take the base rock to become live rock if I add it to my fowlr tank/sump?

 

As long as your current setup has a well established colony of beneficial bacteria/algae it shouldn't take long at all. You will be able to see the rock change and look more like the rock currently in the system. I would say maybe a few weeks would be plenty of time. Once all the "new" rock looks established like the rock that's in the tank now it would be good to transfer it... I would try to use some of the smaller pieces of rock that are in your tank now also, if possible.