I’m have the same issue with an LPS dominant tank. I’ve manually removed the GHA and water changed for over two months now and feed less. I bought rowaphos and a reactor, but have yet to use it out of fear of dropping PO4 to the point of hurting the coral color and growth. I’m so pleased with the health of my corals right now that it’s holding me back from using the rowaphos to eliminate the GHA once and for all.The GHA is probably using phosphate as a food source and therefore giving a false zero reading.
I would look at methods for phosphate removal, personally I use rowaphos (GFO) but you will need to change it frequently to start or it won’t work as It may leach out of the rockwork as the levels in the water get lowered
You don’t want zero nitrate (good general guide 5-10) but you want very low phosphate (less than .03) but that’s got to be a real number, not after the GHA has had its fill. Basically starve it out.
Any suggestions in balancing both?