Most of the activated charcoal or carbon in the filter media are of low quality and need to be changed every 2-4 weeks, however, carbon is not needed in my opinion when a water change will do the same thing.
Activated charcoal-removes tannins, odors, medications, heavy metals to name a few....
When I used store bought filter media I would cut a slit in it and dump the carbon out and save for later if needed and I would use my filter media until it was falling apart only changing it 1-2 times a years. I would give it a swish/rinse in old tank water with a water change to get the bigger pieces of gunk off 1-2 times a month or if the water flow slowed, now I make my own filter media with polyfill I get in the craft department for pennies.
When you only have a couple of tanks to tend to and you have the money to spend-Activated charcoal is fine to use IMO- but it needs to be changed as per the labeled directions.