I cant tell you exactly what they are, you will have to wait for someone more versed in planted tank chemistry than I, but the carbon will remove certain macro, and micro nutrients that the plants need to thrive. This is especially bad if youre paying good money for a fertilizer, just to have some of it removed by the carbon.
My advice (and most everyone elses here) is to not replace the carbon from this point. After a couple weeks it wont be doing anything, as it will be used up. Then instead of replacing it, keep it on hand just in case. You never know when it will be necessary to remove medications from your water.