CO2 needle valve and unstable bubble count

[morganatlanta]

I seem to be having trouble getting a stable bubble count from my standard Milwakee regulator's needle valve.

I'm trying to get a Koralin reactor set up and dialed in, aiming for their suggested 10 bubbles per minute (on the reactor bubble counter, not the one on the regulator), but every time I get the right count, a few hours later the bubbles have slowed significantly (like to four bubbles per minute from ten). So, I have to open the knob ever so slightly to get the right rate (it is very sensitive), but then the rate drops again in a couple hours. I've got the second gauge reading 15 psi, but had the same trouble at 30 psi. This has been going on for days. I've probably been through this cycle 20 times.

The 15 psi seems stable once set, so I don't think there is a problem the regulator itself. I'm wondering if the needle valve is bad or something. Anyone had this experience?

 

[schwaggs]

10 per minute seems very slow to me. I have mine set to 20 PSI, 1 or 2 bubbles per SECOND but use a pH controller to turn the CO2 on and off.

 

[morganatlanta]

How often is it on vs off? I was trying to get it stable running continuously.

That bubble rate is what Koralin recommends as a stating point. I figured I go up from there as I get a handle on my calc/alk consumption rates. Loading is pretty light now as most of my stuff RTNed about six months ago.

 

[schwaggs]

The on and off rate of CO2 when using a controller is dependent on the effluent flow rate. Mine is set for about 150 ml per min and my CO2 is on for about 15 mins and off for about 45 mins.

Without a pH controller on your setup, you are chasing 2 variables at once, pH level in the reactor AND flow rate. Increasing flow rate or increasing bubble count (lowering the pH in the reactor) will increase CA/alk dosing into your system and vice versa. Alternately, increaing one while decreasing the other can offset each other. Finally, the mechanisms to adjust flow and CO2 are inherently inaccurate over time (as you are seeing). It is for these reasons that I reccomend using a pH controller to regulate one of the variables (pH) on a CA reactor setup.

 

[morganatlanta]

I was hoping to avoid the maintenance of a pH probe. How often do you have to pull it out and recalibrate it?

 

[schwaggs]

A pH probe in a reactor does not need to be calibrated all that often. I only calibrate mine once, when I set it up and maybe once a year, if that. The reason I don't calibrate it is that the an accurate measurement of pH in the reactor isn't really important, a relative measure is just fine.

 

[ff337]

PH probes should be calibrated every 6 months. Per most manufacturers.