Nice tank set up and welcome to the hobby. I just wanted to share with you that with a new tank comes stages of good bacteria growth. During the first year of a tanks life it will go thru stages of algae blooms such as diatom, hair algae, cynobacteria, they occur to help build up different beneficial bacteria which is where a well established tank comes from. You can minimize these blooms by doing your regular water changes and just making sure you use good rodi water and don't over feed. The less you do this the longer the stages will last. When it comes to diatom tho...which it looks like with the brown stuff on your sand and rocks.. and I know it's very tempting but leave it. The diatom thrive off of silicates which are in silicone..sand.. The more diatom you have in your tank the quicker it will consume its food (silicates) the faster it will starve it's self out and go away.