cyano in new tank

Newbie reefer here. Recently, I've been battling a brown-ish growth in my sand bed. I suspect it's cyano due to the presence of small tendrils, but its brown so could it be diatoms? Its a 75G, currently stocked with 2 ocellaris clowns, 1 royal gramma, 1 firefish, 1 starry blenny, and 1 pajama...

Do you all think this is the beginning of Cyano?

So I have been running this tank for around 2 weeks now (with fish) four weeks without. 2 weeks after I added the fish I noticed this lighter purple algae (I think it's cyano). It would be great to have an ID on this algae/bacteria (aswell as a few other potential pests). I found it odd as this...