What kind of lighting do you have? What are your parameters? How long has your tank been set up? What is your internal flow rate? What is your live stock list? What is your salinity?
Sorry for all the questions, but to determine if there is a potentially hazardous situation, we need to know these things. Looks alright for now, but should become larger and bushier in a few days. If it shrivels up to nothing, it's bad. Hope this helps.