When I ran a reactor about a decade ago, I set it up to run without a CO2 controller. It took a lot of trial and error, but eventually I got things to settle on about a 6.7 pH in the reactor with a steady-ish bubble rate (that I generally had to adjust on a daily basis, which got annoying over time).
Fast forward to today. I've been running a reactor again, and liking the results (yay SPS growth!). I run the CO2 solenoid on the Apex controller and I've set the control to turn on at 6.7 and turn off at 6.5 (hopefully so so settle on 6.6 as the "average" pH in the reactor). I've then tried dialing down the CO2 feed to as slow as I can muster whilst still being strong enough to be steady, yet fast enough still that I can see the pH in the reactor decrease when the solenoid is on.
As with the natural tendency when you have a controller that can chart things over time though (ok maybe I mean, when "I" have a controller, STOP JUDGING ME), I started looking to how many times the solenoid is kicking on and off, and it's about 60 cycles per day.
Here's a chart of the last hour, for example:
reactor_co2_ph.jpg
You can see that when the reactor output hits 6.7, the CO2 turns on and runs for about 5 minutes. This is enough take the reactor to just above 6.5, then the CO2 turns off and it takes between 15 to 20 minutes for the pH to slowly creep back up to 6.7.
This works out to close to 60 on/off cycles per day. Is there any risk of overusing the solenoid at this kind of rate? Should I endeavour to slow down the CO2 flowrate even further ... or maybe slow down the reactor effluent rate? The reactor itself is an old Wendell-made unit using a John Guest valve for flow control, which doesn't lend itself well to really fine adjustments.