What is the purple stuff on my live rocks and how big will it grow

Question

What is the purple stuff on my live rocks and how big will it grow

Answer 1

alot of things that grow on live rock are purple.. you need to be more specific..

flat and hard- coralline algea, spreads continuously, people want this

kind tree or bush like- formaniferans, a type of sponge, not bad, not good, stays tiny

feathery- some type of red algea, again a neutral thing as long as it doesn't get out of hand,

small kinda flower like with fingers- either a type of rock anenome or zooanthid, good or bad depending what it it, can spread quickly

Answer 2

As was mentioned it could be coraline algae, however there are many things including coral that will grow from live rock.  Some sargassum, micropipes just to name a few.

It depends on the TYPE of rock you have and where it was created or harvested.