Just to add to this. I am really careful to not strip the tank since I did that before and it caused problems. So I use 1/3 of what is recommended by BRS. It only really lasts a couple of weeks before it is depleted, but the tank wont strip that way.
I used to. I was running biopellets and gfo / carbon mixed together. I was dropping my phosphates too low and now just run a small amount of pellets and carbon for water clarity.