I have a Brita filter and it looks like it uses Carbon. It states it has 2 filters built in.
The first one reduces:
Lead, Copper, Mercury, Cadmium, Benzene, Toulene, & Tetrachloroethylene.
The 2nd. one reduces:
Chlorine, Taste & Odor, Particulate-Clas V, & Zinc.
Nasty sounding stuff!

Makes you wonder what we are putting in OUR bodies!
It also states that it keeps a healthy level of Fluoride. I wonder if fluorided is good for goldies? They don't have any teeth!
I never used it for my goldies but I can tell you that the filtered water tastes great!