Now seeing your tank (which is nice btw!) this give a lot of insight.....Aside from the Ludwigia I pretty much see a ton of heavy root feeders I would be investing more in possibly root tabs than dosing a ton of Easy Green TBH. I also wonder what your light schedule is also because from the algae I see it looks like you have a ton of light going this would also be feeding into the low nitrates meaning the longer the photo period the more nutrients taken up. I would look at the lighting and possibly doing less/smaller water changes to get your water more nutrient rich.