I used the BRS dosers for a while(basically the same as the drew's), and to program them for the apex I liked to use this site:
https://www.reeftronics.net/adpg/dosingcalc.php
Just inpout the speed of your doser, the amount you want to dose, and any time you would like to start(like starting during the night and stopping during the day), and it gives you the syntax to put into your apex.