Hello,
Any carbon should be changed as often as possible, preferably no more than 7 days.
The reason is bacteria.
Even if the pores of the carbon are not clogged with waste in one week, they will be clogged / colonized by bacteria, and it will stop working.
To see this effect best, watch the video of the zeolite being shaken in the zeolite reactor and how many bacteria are flying out of it. As a rule, the reactor is shaken once a day, and each time a lot of bacteria fly out of it.
The same thing (colonized by bacteria) happens with activated carbon, especially if you dose carbon to promote bacteria.
IMO, when the manufacturer says to change the carbon once a month, he is a little disingenuous.
2-3 days - is really good solution. it is better to use small portions but change more often, since in a week there will probably not be a single pore without bacteria, if you dose carbon, I think this process will be accelerated up to 2-3 days.