Dick wrote:

I remember comments made that suggest charcoal is not always good to
use in a filter.

I wonder what the pros and cons are?

I have fresh water tanks. All tropical, wide varieties of fish
species.

Current thinking among a lot of experienced folks is that we can't think
any reason to use activated carbon in a healthy tank except:

* To remove yellowing due to fresh driftwood (the
color causes no harm. Some people don't like it)

* To remove medication added to the tank
(water changes are quite effective here!)

* To help remove toxins in an emergency (I once
lost some fish due to fertilizer or pesticide on
some zuchinni skin. I used carbon and big
water changes once I figured out the cause)

A healthy tank has a mature biofilter culture going in the filter, the
gravel, the plants or some combination of the three. Since we all do
lots of water changes and use water conditioner, we can't think of other
uses for carbon.