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.
