The "feed pump" provides the pressure to push the effluent to your tank. Generally a MaxiJet..you want low pressure.
Count the bubbles per minute and the drops per minute on your effluent. You want the effluent about 6.7ph or so.
The most important thing is to get your tank at perfect PH, Alk, Dkh FIRST and adjust it up/down with B-ionic between adjustments on the reactor every 12-24 hours.
IE, you get your tank perfect. Start with the recommended bubbles and effluent in drips or MLs from the Manufacturer. Run it 12 or 24 hours. Retest everything.
If your parameters are HIGH dial the reactor back in the same ratio of bubbles to effluent to keep the ph of the effluent the same.
If your parameters are LOW dial the reactor up some and add B=Ionic to bring your tank back to "perfect". Run another 12=24hrs...and so on until you run 24 hours and it's still perfect.
TT
Killed my first coral in 1991, have tried to do better since. Always tricky.