Depend on how sever the po4 and how fast you want to drop it, I would start with half the recommended value passive, then if u want faster action 100% of the recommended dose passive.
Then when you feel comfortable you can move to reactor.
As an example I now know in my system using a full dose in a reactor take my po4 down from 0.1 to 0.05 in 3 days to a week top. Bow days I do not even test po4, once icp showing me value I do not like, I add rowphse to my reactor for a week then take it off...
The important thing here is frequent testing when you use it the first couple times.
This media will keep taking out po4 and supposedly it will not leach it back when it reach its capacity, as you have seen by now the capacity of this media is massive compared to its volume, so testing is important at early beginning of getting to know the media impact in your system..