<a href=showthread.php?s=&postid=7716510#post7716510 target=_blank>Originally posted</a> by philagothos
Just a thought, live rock is not special and great because it is covered with purple algae. What makes it "live" and beneficial for the tank is the bacteria that grows inside of it. It would be possible to have a rock completely covered with coraline and still not have an effective amount of bacteria inside the rock.
In fact, some argue that although pretty, coraline is actually a bad thing because it covers the pores of the rock making it less effective as a biological filter.
The question of how long from base rock to live rock really depends on how you define your rock as "live". Coraline can be induced to grow rather quickly (month or two), but the bacteria will take longer (up to a year). One way that might help speed this up would be to pulverize a pound or two or live rock and poor it over the base rock. This would directly introduce the bacteria to the base rock instead of having to wait for it to migrate.
Just my thoughts, hope it helps.
-Kevin