Few questions

i have the same problem they tell me it is dead alge i get rid of it when i do a wc but it keeps coming back and noone has told me how to keep it away...i think live sand was a bad choice next sw tanki do im not useing it just LR. but it is not harmful in anyway just suck it out when you do a wc i do once a week

its diatoms. every new tank goes through it. just let it grow and it will kill itself off by using up all the nutrients it needs to grow. sometimes it gets pretty thick before this happens but its not hurting anything. Totally normal.

Yep just diatams, a type of tiny brown algae. Totally normal part of the cycle. Yours doesn't look too bad so I don't think you have any nutrient problems just the tank going through its algae cycle.

If it sticks around for weeks then you might have some kind of nutrient or flow issue but at the moment don't worry about it, it should go away.

I would add some crabs and snails to help clean that up, but to just agree with everyone else, that is 100% completely normal to get that the first couple months of a new saltwater tank.

As far as fish though, if want to put in a fish, add only 1 fish, and make sure it is a hardy fish, like a clown. Do NOT get a damsel though (I know, clowns are damsels, just don't get any other type of damsel. ), you will regret it. Everyone usually gets a damsel at first because they are so cheap, $5, to test out their tank to see if it is ready and then when they want to add another fish they have to tear their tank down just to get the damsel out.