Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Fish and shrimp do not seem to mind fertilizer that raises nitrate. If the current NO3 is from the food you are adding for the fish and shrimp, then you can also assume there is a small amount of phosphate and most trace minerals.
Fish food is low in potassium and iron.
You could put a few root feeder tablets in there, and see if the plant growth improves.