For those not using a dosing pump, but otherwise automated dosing thingamajig...

[JPotter]

Thank you..now is 2 part dosing something one does when using a Ca reactor? I only have mine on for 12 hours at a time as I worry it will lower pH and I seem to find it hard to keep my pH at or above 8.

[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).

[JPotter]

Thank you. My tank came with a Ca reactor so I have continued to use it. Ca and dKh seem OK but the pH runs 7.8-8 which I had thought was detrimentally low. Thus I ran it only 12 hours hoping to stop the drop to 7.8 (that didn't happen). I run my effluent into a "cup" which overflows into the sump. The cup has a pH probe that is always on and runs 6.5-6.7. I had the effulent rate constant at about 60 drops /min (double the CO2 bubble count). If the tank pH is not an issue then I should be comfortable with how things are working and just use Ca and baking soda to adjust Ca and dKh as required.
Thank you for the explaination and numbers

[Delphinus]

7.8 is perfectly fine, IME/IMO. Were it me in your shoes I would leave your reactor on fulltime and call it done. Sounds like it's working well for you.

FWIW, I've found that tracking pH in the tank itself to be of minimal value. (Tracking the pH in the reactor OTOH is of utmost importance. But the tank itself, not so much.) It doesn't really tell you anything specific, but instead is a sort of "resultant" based on other parameters which come together in concert and then forms a pH value - it's better to track those individual parameters because they tell you more - your nitrate is up, your nitrate is down, your calcium is this, your alkalinity is that .. your magnesium is such and such. And so on. I haven't bothered testing pH myself in years, except for when I've had to answer the inevitable question on forums: "What is your pH?" when asking questions on other things. HTH!

[Skimmerking]

Just remember the most important thing here that its a Alkalinity Reactor, and if anything that you should make sure that your alk is stable then out of any of it. your tank can get stressed out pretty quick with the ALk being unstable.