First by no means take my word on this. There are some regular co2 reactor uses on the board, including Brad and they can speak better of this than I. Trying to remember what I ran mine at but it was a long time ago,
I thought it was close to 14psi but would need to find some of my old threads to check. I did find info thread from Melev,s Reef, {the worlds best source of information},
.
http://www.melevsreef.com/calcium_reactor.html
Check it out for now perhaps, until some season reactor users get their two bits worth in.