It's normal for PO4 to sky-high now... as for NO3... normal although didn't expect it to appear so soon... don't worry bro... with your water volume and water flow... things will go back to normal pretty soon A denitrator is quite inevitable for your case as you can't possibly keep enough Chaetomorpha to export nutrients... if you are planning on biological method denitrator... the higher the NO3 in your water, the faster it will run-in