The algae I see is likely diatoms and associated often with a new tank feeding off silicates from new sand and rock. More about diatoms:
iatoms are a brown algae that typically appear in a reef tank that has just completed its cycle but they can also appear in an established reef tank. They can cover sand, rock, pumps, glass, you name it. Diatoms look ugly but in most cases they are harmless so the key is to not panic when they appear.
Diatoms feed mainly off of silicates but also consume dissolved organic compounds, phosphate and nitrates. Unfiltered tap water can contain silicates and is a good way to jump start a bloom if you use it to mix salt or to replace water that evaporated from the tank. The best way to prevent this from happening is to filter water through a RODI unit, although you can still get a diatom bloom when using RODI if the cartridge that removes silicates expires.
Diatoms are typically harmless to a captive reef and can be beaten once their food source expires. Once you put the kibosh on the source, the outbreak should last a couple of weeks so just be patient and it will pass.
To prevent their return, practice good aquarium husbandry by doing regular water changes, keep the substrate clean, don’t overfeed the fish, ensure your skimmer is running at an optimal level and rinse out filter socks and sponges on a regular basis.
Some cleaner crew to help control it are : Cerith snails, Nerite snails and Trochus snails and also Astraea snails are effective at removing diatoms.
