algae crash

Hi everyone! I need some advice and this is the best place in the world for high quality reef advice, so please bear with me and thanks in advance for your help! Basically I was skimmerless for a couple of weeks after removing my previous skimmer to prepare the sump for a skimmer upgrade and...

What is this stuff and how do I get rid of it? Will this kill my corals? I have RODI water and have been doing water changes. I am so worried it will take over and kill everything.

It is my first post in reef2reef, every day I read and learn from this wonderful site, and although it took several years in the hobby, now I like I'm back to start and do not know what is happening .... I started this tank 75g using products of "aquaforest" probiotic reef salt, my water is ro /...