I think it depends on the type of reactor and media that you are using. Generally, if I remember correctly, you want the PH inside the reactor to be at 6.7 to 7.0. In order to do this you need to play around with two settings (bubble count and drip rate.) On top of that you have to check the calcium and alk levels in your tank over a few days. This way you can see if the reactor is set properly to maintain the levels necessary for your set up.