Looks like you have some type of Caulerpa (also invasive and near-impossible to irradiate (thicker green branch across the top). Need to see the 'leaves' or 'bulbs' to give a more specific ID, just one long stem there. Also looks like you have halimeda (a calcifying leafy algae whose roots aren't as strong/resilient as caulerpa) - this is manageable though but you have to out-work it by picking it regularly and eventually it'll give up. Between the red algae and caulerpa, I'd probably go straight for a long term (think permanent) course of Vibrant if you don't wish to restart the system. Only once major elements and nutrients have matured/stabilized. Just my opinion. Those algae can be A LOT of work.
