on reefkeeping magazine randy has a convenient dosing calculator for dosing the first time and for daily dosing subsequently. it depends on the size tank and corals. i bought the dowflake at a hardware store on 12th and monroe st, n.e. in dc. i bought the magflake at the home depot on rhode island ave. my calcium went from 220 to 450ppm with one dosing. i have only been using it for a week but so far my alk and cal has been more stable then what i was using before.