Ummm...I don't know what everyone else is particularly thinking but the pink on the sand is the start off of good bacteria algae called red algae/purple algae but often looks more purple in the tank. It is stemming off of your live rock which also has it on there. Do not I repeat NOT get rid of it is a very beneficial coraline macro algae that actually does not harm the tank at all and you should want this algae to grow more then any other.