I had both those algaes come on my box of Figi rock. When it was in my old FOWLER tank it took over because of high nutrients and poor filtration equipment and too much lights (come on I was just starting out!
). But now a year later in my reef tank it's going away and mostly non existant. Now when I prune it it doesn't come back. Sargassum is now totally gone aswell. The dictyota I HATED it was so ugly and grew like mad but now with low nutrient levels and good equipment it's fine. I've read that sometimes sargassum just stops after a year, give or take. I think you should be fine you have a nice system.