Larva rock is not inert, meaning it will break down releasing minerals and increase your water hardness and possibly even raise your pH.
Marble in the other hand is inert and will not effect your water parameters.
In either case a 10% daily water change will supply you with ever increasing nitrates and bacterial counts putting the health of your discus at risk. Any partial water change schedule that does not replace a minimum of 100%or the tank volume weekly is inadequate IMHO