I don't use the red sea NO3PO4X, but I do use Prodibio. I have had nice results with this product and only have to dose it every 15 days. They make large ampules these days, so it might work for you. Have you tried to track down other causes of high no3 other than your bio load?
I have a similar size system with similar load. huge fish.. huge skimmer
I dose about 10ml of no pox..every system is different. You have to dose and test
If you dose too much you will see these red bugger like things forming in your refugium
that is a sign you are dosing too much