PeterC99
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So for ARM media 6.8 is too high a pH and won’t dissolve much, 6.4 is probably about right to start getting good dissolution of the media. So your pH swings in the reactor are too large, you need to keep the reactor closer to 6.4 and it will produce far more alkalinity and Ca. For a calcium reactor to be most efficient it needs to attain an internal equilibrium of CO2 injected, the volume of incoming tank water (flow rate) and the pH of the incoming water, then you will get consistent stable dKh levels in the effluent. So keeping the variables you control (CO2 and flow rate) constant is important to attain equilibrium within the system.
Which brings me to my next point that most “control” oriented aquarist overlook. Having your controller open and close the CO2 solenoid is actually counter productive to this. It’s far more efficient (and actually easier on you) if you keep the CO2 solenoid open and limit the injected CO2 to exactly what you need. This accomplishes several things. An equilibrium within the reactor is easily achieved and maintained (unless you make a change to the CO2 amount or flowrate), pH inside the reactor becomes nearly constant (small daily swing based on the pH swing in the tank from day to night). The reactor can never “run away” from you, (because the only variable that produces Alk or Calcium is CO2) and there’s no pH probe that can and will ”drift” between calibrations. The result is a highly stable alkalinity in the effluent and your tank dKH becomes stable.
I’ve operated my CaRx both ways, and the “old school” manual way is far easier and more efficient. The last 3 years of running my system this way I have only had to make a major adjustment when I change my bottle which is a 20# tank and it last almost a year. (I dissolve about 23-30 lbs of media in that time).
So you are suggesting find the option bubble rate, set it there permanently, and not use the solenoid to regulate CO2? I would turn the pH probe off and just monitor the output effluent?