how useful is the activated carbon in a HOB, i understand that they wear out over a month, but whats the benefits of having them and how do they affect planted tanks. from my initial reading on google it seems that they are only effective for a short time (24-48 hours) and then they just keep things inside the water to be re-released. It seems a bit counterproductive then if there's a lot of HOBs with cartridges that have built in carbon within filters.