running Ca and Kalk reactors together


New member
I made a DIY Kalk reactor and I run a Ca reactor and now hope to run them both, via Apex, to smooth out pH variation. For those of you that do this, how do you do it?

I was thinking it might be a good idea to switch between Kalkwasser and RO water for auto topoff, based on the tank pH (eg 8.1). Maybe I should just use the Kalk for topoff all the time?

My Ca reactor pumps run continuously, and my Apex controls the CO2 solenoid for pH = 6.5 only during daylight. (does it make any sense to turn on/off the recirc and effluent pumps too?)

Would I be better off just dosing kalk intermittently at night based on a pH threshold only?
I am not having any particular alk or Ca problems.

Thanks for your comments.

Special thanks to Randy for the plethora of reef chemistry info he's shared.

Randy Holmes-Farley

Reef Chemist
Premium Member
The usual way is to run full strength limewater to replace all evaporated water, then set the CaCO3/CO2 reactor to pick up all the remaining demand, so set it to maintain alkalinity. I would run the CaCO3/CO2 reactor 24/7. Limewater can dose only at night or 24/7. I dose 24/7, but I do not have a CaCO3/CO2 reactor.

Even though you have the capability, I wouldn't make it automatically change anything based on tank pH, except perhaps for emergency shut off (say, limewater shut off at pH 8.55 and up and CO2 shut off at pH 7.7 or less)


ReefKeeping Mag staff
Premium Member
I'd let them both run 24/7 with the solenoid controlling against a ph high point unless there was a very big diurinal ph swing to manage with kalk at night only.
I'd also start with the kalk and let the Ca reactor take up the slack unless I wanted to lower ph, in which case, I'd lighten the kalk saturation and increase the CA reactor output.
Once they're tuned in and balanced to the system's needs for calcium and alkalinity and acceptable ph ,it's better to just let them run rather than on/off methods,ime.