Hi Leean, welcome to MAAST.

Every new tank goes through some natural startup algae blooms. The first are the brown ugly diatoms, unless you like brown that is. If it appears coagulated into little shapes, that can be the work of competeing bacteria colonizing the glass and rocks as well as micro organisms that live on the diatoms or construct tunnels with their empty cell membranes making a place for more little diatoms to grow easily in the shape you see. Nothing to worry about, but, certainly a motivator to think about adding a cleaning crew when your tank is ready. There will be more algae blooms that will annoy you but, just take it all in stride for the first several months. It has to happen to get the nice tank you want. It will be fine in the end as long as you use the correct wave length of lights for salt water tanks and have that clean up crew added eventually, and of course, use RO/DI for make up water. It also helps to have plenty of water movement, no stagnant spots. Do you have a refugium to grow macro in or a sump with this tank?