activate carbon is made in various ways with various chemicals in order to reach a blend of absorbive material thats safe for use. theres no real general rule per say, all manufactures have different guides for different grades, however no one product will act in the same manor if its from a competitor with a different manufacturing process. It all comes down to contact, product purity & water parameters. logicly we all have different flow rates, & there are many ways to use AC, so manufactures provide guides based on R&D findings & potential product shortening so you buy more..lol
Crap stuff can last a week, quality can last a few months. Only you & the labs can determin that! If your water quality visually
drops your load could have increased, your carbon needs replaciing or theres a reaction with your additives & your water parameters.
Choices of passive or proactive are yours alone bud. Although its a no brainer to realise AC absorbive potential is governed by the volume it comes in contact with, so having water pass through the particle matrix instead of majority around it is far better. i suggest over sizing the amounts used, then after your own pre determined time, ether leave it out of the system for awhile or if you prefer replace it. Keep in mind its based on the animals you keep as well. AC can indeed trap the elements for forked over the counter to add to your tank to begin with.
kinda like robbing peter to pay paul if you will!
