Cured or uncured? if its cured you can add small amounts and watch your water for spikes in ammo- if its un cured you will need to cure it then add in small amounts and keep checking the water still.
whipple said it, i would say 20 lbs at a time(in a 120 gallon), but if it is MO'ed, i would cure it in another container fisrst, to be sure, often there will e die off from shipping, and i feel it is better to be safe than sorry
