This is what you need to run a reactor:
Ca Reactor
CO2 tank
Regulator/solenoid for CO2
air tubing or CO2 silicone tubing
Ca Media for reactor
Check valve between the reactor and regulator, some reactors come with a check valve. Mine did(Korallin 1502)
pump to feed reactor/unless you gravity feed it
and lastly I would stongly recommend a pH monitor/pH probe, it's not absolutely necessary, but it makes it much easier to manage.
This is what I use:
Korallin 1502 reactor
10# CO2 tank
JBJ reglator/solenoid
silicone tubing
Koralith medium size Ca media
Industrial check valve came with my reactor
aqualifter pump
Pinpoint pH monitor/probe
I use a drip cup for the effluent to place the pH probe in and to take Alk readings. Depending on the type of media you use, you want your effluent to have a pH between 6.5 and 7. Saturated effluent should have a dKH of 34. You adjust your BPM(bubbles per minute of CO2) and DPM (drips per minute of effluent)to adjust for changing Ca/Alk as needed. The more BPM, the lower the pH in the reactor, the more Ca/Alk released at that same given effluent. You increase both the DPM and BPM if your levels are not being maintained by the reactor with the current settings(BPM/DPM) The goal is to have the slowest/lowest effluent, lowest DPM, and highest Alk effluent that will meet your systems needs. There is no magical formula for dialing the reactor in as far as DPM/BPM, as the incoming water from differnt systems have different levels of Alk/Ca saturation, and the load on the systems are different. The goal is to maintain Alk/Ca. So you must first have your levels in line, and make sure not to dose anything else when attempting to dial the reactor in. If Alk levels in your DT are dropping, your effluent either does not have a high enough dKH(it's not saturated because their is not enough CO2), or you don't have enough effluent passing through the reactor.
Without a doubt, my Ca reactor is the best piece of splurge equipment I have bought for my tank. I dosed saturated Kalk and a lot of high purity Two Part for several years. The reactor has made my life/tanks life much easier and is definitely a worthy investment if you have a decent load on your tank, and/or are just tired of the maintenance of dosing chemicals every day/several times per day. If you are out of town for several days, no worries...