are you talking about coralline? other than "reef" type lighting maturity is all it really takes (yes adequate calcium levels but with regular water changes unless you have a reef system with SPS you really shouldn't need to do a lot of supplementing). I didn't have any for the 1rst year of my tank being up. switched it from FOWLR to reef and within 3 months every rock was purple. Rocks that had NO coralline before. All you need is one rock that has decent coverage and it will spread. dont know why but it tends to grow much easier ande faster in a reef setting (perhaps due to more rigorous maintenence of calcium and trace element levels. perhaps because reef tanks usually have more optimal lighting. perhaps both). I have a book that says it flourishes under heavy actinic lighting but I've only heard that from one source.
If your talking about other stuff like feather duster, sponges, other worms and such depends on the rock you started with and tank livestock that doesn't eat it. that kind of stuff tend to come and go based on water quality once the tank is established.
