laterite?

im about to begin my first planted tank in a 55g. i have the red sea
co2 setup, 4 40watt flourescent bulbs, but the red sea substrate was too
expensive so i settled on this box of laterite from petsmart. i have no
idea what it is but i followed hte directions and mixed it into the
gravel. so my questoin is, is this laterite stuff any good? it seems i
have to periodically add new laterite, how do i do this with an
established tank without messing up the roots, etc? also, what plants
do i start off with? anyone have online sites to order in bulk from for
cheap? thanks.