To starve them out, my suggestion is to get them down to .01 or a trace and have you nitrates at 3 to 5 to starve them out for two weeks. Then bring the phosphate up to a .02 and see how the tank looks. If you want to get the phosphates down fast us a product with Lanthanum Chloride in it. Run GFO as normal. Are you running as filter media such as sprox, life bio fil? I run the life bio fil with a little zeomix to keep my nitrates in line, for the reason I feed heavy for the corals and I have fat fish
I don't think that's a good idea. They strive in ultra-low nutrient systems and quickly take over the entire tank, within 24-48 hours.