You must export the nutrient to get the nutrient level to drop when you add carbon. This is why strong skimmer to get the bacterial out of the water column to decrease nutrients. You can definitely add some carbon to get the bacterial population to increase and this would hopefully improve the food availability for animals in the tank, assume that the tank is diverse enough to have all the various animals that feed on the bacterial then in turn get eaten by animals that are higher in the food web.