A standard 55? 48" long? If so then you will need about 80lbs of sand to obtain a 2 inch sand bed. Most people will "shortcut" the sand bed by getting dead sand, just make sure it is fine grade, Aragonite sand is best, then add live sand on top....no need to mix, just let it be, smooth it out and it will seed the dead sand in no time. 1 bag of live sand is sufficient. (25lbs)