infected tank

i recently added a few pieces of live rock to start seeding my base and after a few weeks a few balls of white stuff popped up around some of the base of the rocks. any idea what it is, how it got there, and what i need to do? thank you - justin

all of the fish in my tank have died off due to what i think is ich.... could have been something else like velvet or the clownfish disease (cant remember the name) two were clowns by the way.. My ? is how long should i wait until intorducing new fish? i have one fire shrimp, basic clean up...