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CO2 flow control

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I have an ongoing struggle controlling the flow of CO2 into my CA reactor.  I set to bubble rate of maybe 3 per second and then over time it decays.  I understand why this happens.  The reactor becomes pressurized and the differential pressure across the needle valve changes decreasing the flow.  You have iterate on it to get stable and then it still very touchy. 

I just upgraded to a reef octopus reactor that has a Ph probe port on it.  I am thinking that I might just control the CO2 flow using the Ph reading and cycling the CO2 on and off with an more aggressive feed rate, with a min time on and off not to over cycle the control valve. 

Anyone else have in clever ways of dealing with this.  The correct way is to use to a CO2 mass flow controller but they cost at least a $1000 dollars.   

I would also be nice to measure the effluent rate so I have feedback. The Apex 1/4" flow monitor is a minimum is 3 gallons per hour,  1 gallon is about 15000 drips so to little flow to use it. 

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You could be on the lookout for a used Carbondoser.  While not cheap, it is half the cost of the $1k mass flow controller.  I see them once or twice a month on R2R for $150-$200.  You set the number of seconds between bubbles from 1-10 and it takes it from there.


I don't know if they even make them any more so used might be the only option though I see a couple places still show them as in stock, but that was the direction I was headed until I got a saturated CO2 style reactor.  There might be another brand that does something similar, I haven't researched it.

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You know my answer.   I control CO2 flow based on target pH inside the reactor (using a dedicated probe).   Just turn the solenoid on/off.  

AND, also disable based on overall Alk of the system.   (If Alk > setpoint, turn off CO2 until the next test cycle)


  • Fallback OFF
  • If pHCO2 > 6.50 Then ON
  • If pHCO2 < 6.30 Then OFF
  • If Alkx5 > 9.00 Then OFF
  • Min Time 005:00 Then ON

One week viewpoint, You can see the obvious cycles when Alk is >9, and pHCO2 floats up to 8.


Zoomed into the June 5th window.



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1 hour ago, Krux said:

Do you just run the co2 through a Neptune solenoid to achieve this?  Seems pretty simple.

No, not a neptune solenoid.  A classic CO2 regulator, with needle valve/etc, with 110v solenoid control.   And fed by a basic EB832 outlet.  Easy Peezy.

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Same here.. I turn on CO2 based on pH and raise and lower my pH set point based on calcium level.  Beats the heck out of bubble counting.  I set my bubble to 1 per second and just let it dose until the calcium reactor reach a set point.

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Posted (edited)
On 6/7/2024 at 10:03 AM, Stephen Sturges said:

Krux,  so is the saturated reactor just running at a constant pressure to maintain a certain partial pressure of CO2?

Correct.  See Deltec Twin tech (too large for my tank or I would get one) or the Dastaco - I have the C2.  I don't know if there are other brands outside of one that is down in Australia, I think Dastaco has curtailed production due to a law suit from Deltec.  Lots of them floating around though.


As Rudy pointed out, these are both 6 ph melting reactors, I use marble chips.


Here's a review by Jake on the Dastaco, the video is my actual model.



And another one on the Deltec


Edited by Krux
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