| Definately sargassum, more than likely the Lobophora variety. It's not an indicator of your chemistry being off, rather that things are going well. It's not really useful for nutrient export, but is a nice addition to the tank.
I had some growing in my 7.5 at one time and it was a pretty fast grower until I introduced some red leg hermits and an emerald crab that made short work of it |