| | Re: carbon or no carbon
Carbon is beneficial at first to absorb excess ammonia or other pollutants, but it is not necessary if the tank is very heavily planted. After a tank has established, it's not generally recommended. You also don't want to keep old carbon in the filter for an extended period (months or longer) because it will gradually begin to release the pollutants that it has absorbed. I don't think there are many formal studies on whether or not it will absorb fertilizers for the plants...but I don't think it would have much affect (just guessing though).