I just had the same problem
mines took over 70% of my tank, it will take over if you let
it is like a weed.
what I end up doing was taking out all the infected rocks and trading them for clean live rocks.
I guess the best thing to do if you want to keep this stuff in your tank is to put it up real high in the tank and if it start speading (which it will) you can just take out that piece of rock it's on
Good luck