hi.
Most people I know only use the monitor/meter and not the controller. They also don't use the solenoid, but instead, run the reactor 24/7. It is more work, but basically you have to adjust the reactor with a pH meter until the CO2 is use efficiently, while both the alk. and Ca are in good state. When using a new Ca Rxtor medium, they may need to use the meter to fine tune the Rxtor again, but other than that, they only use it to do periodic checks on the tank pH once a while.
You don't need to have two pH probes soaking in the tank all the time. Beside they are expensive to replace. However, it is nice to know the pH anytime just by looking at the up-and-running meter. Also, some people like to use the controller/solenoid combo. it is like personal perference.
Common mistake is to give up too easy (ca rxtor is not the easiest equipment to use) because of frustration. Another one is to bubble the CO2 too fast and cause air pocket within the reactor (may stall the pump, depend on the rxtor design). Another one is to expect the parameters to be perfect as NSW, especially the Ca. However, the fact of the matter is ca rxtor is useful as a ca/alk stabilizer, not something you can use to get the Ca from 250ppm to 400ppm overnight. Again, patience is necessary, just like other thing in this hobby.