CC is a byproduct of the FC breaking something down ... the CC is then broken down by more FC or the sun.
If you see a high level of CC, it means there is something in the pool, but it is not definitive because sometimes the CC are broken down quickly as well ... thus the requirement to also pass the OCLT.
High CC means there is certainly something in the pool. Low CC means there may not be something in pool, the OCLT confirms there is nothing.