Magroves are slow growing, hence slow on the PO4 uptake. The best macro algae would be Chaeto. Ask Biff to send you some of hers. If you have a sump with a refugium, you place it in there. As it grows it sucks up phosphates and you trim it back.
Lots of people are going the algae scrubber route. Do a search for DIY on that. I have not tried this.
And I use a reactor from Bulk Reef Supply that I run High Capacity GFO in (for me this makes the biggest difference)... along with Chaeto in my fuge.