Activated carbon does not leach stuff back to the water.
I keep some on hand in case of emergency, but do not use it fill time.
I use media in this order, following the path of the water:
In the tank, coarse sponge over the intake.
In the HOB filters:
Blue and white bonded media (Rite Size is one brand name)
Chemical media. (Varies: soft water tanks get peat moss, hard water tanks get coral sand)
Quilt batting = polyester floss.
Bio media, in a mesh bag.