A fully automated dosing system is not cheaper than CA-RX. It can actually be more expensive to start and will cost more in the long run. Large solution containers, reliable dosing pumps, reliable controller, and a salinity probe are essential to make he system work.
To get the best CA-RX system, it'll be more to start but will cost less in the long run. I'm talking about getting the best regulator for the injection of C02 and a continuous peristaltic pump for the effluent. You skim on these two components and it will put you in a reefing nightmare.
Obviously, there's Pros on Cons in the two system. For smaller system under 75gallons, I would do the dosing system. It avoid the PH from dipping and is less of a tank crash hazard. Again, reliable pumps and controller and a salinity probe are essentials. The salinity probe is to avoid the pump from over dosing. You program your controller to shut off the switch/power supply of the pump if the salinity is too high from the dosing thus avoiding a stuck-on pump to run.
CA-RX is a set and forget when you dial it in. But it can take some time. PH can be low if you're not careful. You can program the controller to shut off the C02 supply via a solenoid when PH is too low, but it take time for the reactor to shut off completely. Things in the reactor just don't happen right away when you want to. It takes time and many people who started CA-RX quickly give up when they're constantly adjusting things on it.
I've used CA-RX but didn't like the low PH and now I'm on an automated dosing system with all those components mentioned above.
