[Delphinus]

Sorry I missed that question before.

No, if you're already running a Ca reactor there's no need for 2-part dosing. (Well, with a small exception, I'll get to that later.) Similarly if you're already doing 2-part dosing, there's no need for a Ca reactor.

2-part dosing is showing a resurgence in popularity over the Ca reactor because it's simpler. A Ca reactor can be fussy to dial in, it requires pressurized CO2 which pulls down your pH, and it can only add Ca and Alk in balance with one another. It does a better job of *maintaining* levels than it does *raising* levels. So here's that exception I promised earlier: you still have to use 2-part dosing at first to bring your levels to target and then you use the reactor to maintain those levels. In actual fact you are better off leaving it on 24/7 rather than on for 12 hours only, because you want a steady-state situation. If you're finding a reactor is pulling your pH down too much, it is either not dialed in right or it's sized perhaps too big for your system. There's quite an art and a science to dialing it in. More on that later though. About the pH, for the most part it shouldn't be a concern. Whereas a typical reef should run about 8.4 daytime, 8.0 nighttime; a reactor fed tank will be more like 7.8-8.2, 7.7-8.1 or in some cases even 7.6-8.0. These are not numbers to worry about however. If it gets lower than 7.6 though, I would say something is off.

You want your reactor to be set at 6.7. You need whatever bubble rate to acheive this. You want a nominal flowrate of your effluent. A fast drip is usually where you want to start, or up to about 60ml/min. You dose manually to get your Ca and Alk to proper levels, then you leave the reactor run for a week, and test again. If the levels are down, you redose Ca/Alk back to target, and you increase the effluent rate, and adjust the bubble rate to achieve pH 6.7 (a pH controller is nice for this, you overset your bubble rate and let the pH controller turn on and off the solenoid to acheive 6.7. Nice, but certainly not necessary.) If your levels are up then you back off the effluent drip rate and the bubble rate to 6.7. No matter what your effluent rate, you want your reactor pH at 6.7. Anyhow and you test again in a few days to a week, and so on, and so on, and so on, until the levels remain constant.

....

Now conversely, 2 part dosing can achieve easily both level maintenance, and level raising. And it's not too hard to automate, although automation isn't necessary unless you happen to leave your tank for long periods of time and you don't want your tanksitter to worry about dosing. But due to the simplicity, a lot of people are no longer running Ca reactors (I used to, and don't anymore, and likely won't go back to it: I can use the CO2 equipment on my planted FW; and I can dose into multiple tanks whereas a Ca reactor can only be run on one tank).