Anyone running a media vessel buys carbon by the cubic foot rather than in a cartridge, which is cheaper per volume and puts the specification in your hands. Four decisions cover it: what the carbon is made from, what grade it is, how much the vessel takes, and how to keep the rest usable until the next change.
Base material and grade
Coconut shell carbon has a fine pore structure that suits taste, odour and smaller organic molecules, and it is hard, so it produces less dust and stands up to backwashing. Coal based carbons have a broader pore distribution suiting a wider range of organics. Catalytic carbon is a modified material made for chloramine, which standard carbon reduces slowly and incompletely, so if the utility's report names chloramine that is the grade to buy. Specify base material and grade rather than ordering generic carbon and hoping.
Working out the volume
Vessels take a specific media volume plus a gravel underbed where the design calls for one, and the manufacturer states both. Do not estimate from tank height, and do not fill to the top: freeboard above the bed is what lets it expand during backwash, and a vessel packed full sends media to drain. Order the exact volume plus a small margin, since a job stopped halfway with the valve off and the tank open is an unpleasant way to discover you are one bag short.
Storing what is left over
Activated carbon adsorbs from air as readily as from water, so an open bag in a garage steadily loads with whatever is around it: solvent vapours, fuel, damp. That consumes capacity before the media ever sees water. Keep spare media sealed in its original bag inside a closed container, in a dry place away from anything with a smell, and use it within a reasonable period rather than treating it as indefinite stock. Media stored badly is not a bargain.
Loading and the first backwash
Tape the riser tube closed so nothing falls down it, load the gravel underbed gently to avoid cracking the distributor, then the carbon through a wide funnel, and remove the tape before fitting the valve. Then backwash to waste until the water runs clear, which takes longer than expected because fresh carbon carries fine dust. That first backwash also classifies the bed. Note the load date, since carbon exhausts invisibly. Our carbon media replacement guide covers removing the old bed.
Questions people ask about activated carbon bulk
Coconut shell or coal based carbon?
Coconut shell suits taste, odour and smaller organics and is harder. Coal based carbons cover a broader range of organic molecules.
How much media does my vessel take?
The manufacturer's stated volume, plus the gravel underbed if the design has one, leaving freeboard above the bed for backwash expansion.
Does spare carbon go off in storage?
It loads from the air, adsorbing vapours and damp, which consumes capacity. Keep it sealed, dry and away from anything with a smell.
Why is the first water black after loading?
Fine dust from the fresh media. Backwash to waste until it runs clear before returning the vessel to service.