newbie with coral issue

Hi TFT



I recently got my 90l tank up and cycled so at the weekend we went out and bought a mushroom coral and a goby.



Now the goby is doing fine but my coral seems to have some sort of growth that has already killed off one mushroom and another has sprouted up on another which looks to be doing the same.



Its a slimey growth. I noticed today one of the strands had got stuck on my goby but it has since gone.



Here is a pic from a few days ago. Note the big clump in the bottom right. This is the remains wrapped up in slime. It did get cast off later and I fished it out and chucked it.



Any ideas? I will get a pic of the latest growth and victim tonight when I get home.