Quick Answer
Activated carbon (often granular activated carbon, GAC) is a porous medium that adsorbs contaminants onto its surface. It is broadly effective but loses efficiency in hot shower water, which is why it is often paired with KDF-55.
Problem
Carbon is marketed as a universal solution, but its performance changes with temperature and the specific contaminants present.
Product Recommendation
ZOOSHEN Essential and High-Output systems pair activated carbon with KDF media for broader coverage across shower temperatures.