Hi everyone. After noticing what seems to be the beginning of HITH on my festae, I have looked into the whole Carbon thing. I have decided that I don't really need it in my filters. Along with removing the carbon, I am also adding vitamins and increasing water changes. I have an AC 110 and a Rena xp3 both contain carbon. What could I replace the carbon with in the middle layer of the AC 100, as well as the top compartment in the xp3?