I really have no idea pound wise how much is in there. lol. I know I took alot out when i restacked...some went up to the hex tank, some base to the 120g...and i still have quite a bit in my sump in the basement....and i've given some away, too. The green rock nem seems to like high light, high flow. the pink and white rock nem likes low light and a little flow. So...answer to question...guess it depends on the nem!
I just realized i was very little help in answering your questions....wow.