Not to worry thats a new tank.And when the dark slime grows on your live petsmart sand not to worry,its all part of starting a saltwater tank.Diffrent algea blooms can and will happen for up to a year or more.You can siphon scrape wire brush all you want,dont sweat it.Just about when your going loose your mind over diffrent algeas it will suddenly end as quickly as it started.Its part of the game,you can buy some tangs they eat more algea than most other fish.Relax you are right where you want to be,have fun.