Merman

And this is why I have conceded to testing Alkalinity every couple of days.  Good thing I'm not traveling lately.

If you have too much money laying around you could always get one of these: http://www.aquariumplants.com/CarbonDoser-Electronic-Co2-Regulator-p/co2-11.htm?_vsrefdom=adwords&gclid=CjwKCAiAlfnUBRBQEiwAWpPA6dLWvYcee7_r9CHY2xyKkxRoYeyvry4lozFRSy8jZTjMnk3xfNnSDxoCrKkQAvD_BwE

That’s what I use and it works great.

I think you’re getting some really good advice by relying on the regulator rather than the ph probe. If you happen to accidentally set the controller to always on vs auto it should still function normally. I may or may not have made that mistake in the past and melted my reactor.


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I follow a similar strategy. I've tried the slow drip with varied success in the past, but recently has bit me in the buns. The flow went from a steady drip to a very slow drip, alk dropped to 89. Then I increased it back to the broken flow, more of a rapid drip so it wouldn't slow down on me when I'm out of town and alk went to 164 in two days. I haven't even checked it since Friday, but everything looks ok
 
I also don't rely on the pH. I use it more of a monitoring tool to gauge if the flow has stopped from a clog or if the flow is too high. I use a timer for my CO2 dosing (on every half hour for ~20 minutes) and adjust the bubble rate and the effluent flow rate to control alk. This way I'm not relying on a pH probe that can go bad or get a bubble on it and send everything down in a death spiral. There's all kinds of ways to control alk, I've just found this strategy more successful than ones I've used in the past. It's not without it's problems, but it's better than some alternatives IMO.

Dogfish is correct, calcium reactor medias are not the same and will melt at different levels!  I learned that the hard way by melting down my reactor when I switched from ARM to Reborn.

I would expect a linear change rather than a sudden drop off.  You can always measure the effluent alkalinity at different PH levels to be sure but that has been my observation.

In my experience, PH calibration problems are usually caused by an old or faulty probe.  How long have you had yours?  When you calibrate it, does it take a while to settle or do the readings seem erratic while settling?  They definitely have a limited lifespan and I usually end up replacing mine every year or so.

I have struggled with my calcium reactor at times just like everyone else but have learned some tricks along the way.  You might want to consider running your effluent at a much higher rate (you will obviously need to run the PH in your chamber higher too).  I have found that the valve is less likely to clog over time if you have more of a steady stream coming out vs a slow drip.  Fluctuations in effluent rate (they WILL happen unless you're using a perisaltic pump) are also less likely to cause alk swings since the effluent is less concentrated.  You're also less likely to melt your reactor since your set point is now much higher than the media melting point (I've done this several times and it sucks).  You won't be able to count drips/second anymore so I would use a timer/measuring cup instead.  You'll use more CO2 but that's a tradeoff I'm willing to accept.

To give you a reference point, I have a fairly mature 150g SPS-dominated tank with a drip rate of 45ml/min and an internal PH of 6.85-6.9.  When tuning my reactor, I set the effluent rate to a broken stream (between drip and steady stream) and leave it alone if possible.  Then I adjust the PH down (starting at 7.2-7.3 or so) until I get to the alkalinity level I want.  In the future you can adjust the alkalinity up or (hopefully not) down by just changing the internal PH with the controller.

Hope this helps.