Pressure on the reactor would be fine, they are made for that. Lots of people don't even use a pump to feed the reactor, they just tap the return (to tank) line to feed the reactor. Most small pumps would work.
You would add some type of small valve at the output line and there you would dial it so that it drips the right amount of water from the reactor. Dialing it before the pump really would not work. It has to be dialed at the other end (output end) just before it exists back into your tank/sump.
Regards,
Carlos Chacon
CoralVue