Activated Carbon is more efficient when kept in a the mesh bag, but remove the plastic outer packaging. This is due to the fact that it is a absorbent element which is comprised of small piece which can end up all over your aquarium if not contained.
Activated Carbon is most efficient when clumped together as this increases the surface area of water vs carbon surface area.  This allows more carbon to filter the water, removing bad odours, discolouration, and excess nutria and medication.
Activated Carbon is best changed every 3-6 weeks depending on the size, stocking level and specific reason you are using it.
The best analogy for carbon is that it is like a cup. It will fill and absorb until its capacity, at which point it will overfill, putting all of what it has absorbed, back into your aquarium.
It is due to this that we recommend changing it frequently! A frequently maintained aquarium is a healthy beautiful aquarium!

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