help macroalgae

Ok, so Im really new to the hobby, in fact, Im just starting and have only fw experience. I know saltwater is a lot harder. Im attempting a mixed tank of mostly macroalgae (hear its easier), but I cant find any info on whether they can be added during the cycling process, like freshwater...

I got the AI refugium blade which my lfs told me was a good grower this was about 3 weeks ago. My first 2 "golf ball" sizes died. So then I got 3 and this is them right now.this is me after clumping it back together which is now pretty small. Now I have read everywhere saying it might be low...