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I can't get CO2 concentrations high enough

Discussion in 'General Plant Topics' started by banderbe, Feb 22, 2006.

  1. banderbe

    banderbe Prolific Poster

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    I built a "Rex Reactor"- a design many of you are no doubt familiar with- and something is not right.

    I am putting 3 bubbles per second into the reactor which is powered by my XP2 filter, all of which are on my 29 gallon tank.

    My KH is about 18, and currently according to an AP pH test kit my pH is 6.8, but I don't believe that's correct since that would mean I have 85 ppm CO2, and my fish are all fine. The KH value is what is on my city water report and is confirmed by an AP KH test kit. Another reason to suspect the test kit is wrong is that my water's pH after being degassed should be around 8.2 (assuming 3 ppm CO2 for standing water). A test of this water's pH with the same kit shows a color only *slightly* darker than the highest value of 7.6. Still another reason to suspect the test kit is wrong is that I used a brand new Hanna 7.01 buffer calibration solution and tested it and the AP ph test kit said the pH was 6.4. In all cases the test looks to be about 0.6 units off.

    I have seen Tom say that 1 bubble every 3 seconds is sufficient in a 20 gallon tank.

    If I back off that far on my tank, or even just to 1 bubble per second, my pH according to the AP test is between 7.2 and 7.4.

    This is really driving me nuts not being able to tell if I'm getting good CO2 concentration in the tank.

    The plants look *okay* but nothing great and certainly no pearling. They do not pearl after water changes either. The tank has been up for just under 3 weeks, the first two of which I was using "softened" water with a GH of 2 to 3 and a KH of 18. Suffice it to say the plants did not appreciate it so I guess I shouldn't expect them to look great having only been in a tank with normal hard water (GH 22 KH 18) for four days.

    Help!!
     
  2. fosteder

    fosteder Guru Class Expert

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    Re: I can't get CO2 concentrations high enough

    Yeah 3 bubbles per second is insane on a 29 gallon. Evidently you are just wasting CO2.

    Can you see the CO2 bubbles coming out of the filter exit?

    What is your surface movement like?

    Have you tried another method of injecting the CO2 (ie. venturi reactor, or airstone)?
     
  3. colonel

    colonel Guru Class Expert

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    Re: I can't get CO2 concentrations high enough

    I use the same sort of inline reactor on my 75 gallon tank, and I am currently running about 4 bubbles a second or so. At the end of the day it drops my PH down to 5.6 no issue at all.
    But as i am working out in other post I still have BBA, and im not really all to keen on test kits, they have never been helpful to me as of yet in doing anything that benifited my plants, how ever I dont think you should need to dump a TON of CO2 to get good saturation levels in the water, maybe consider the mist method? I dont really want the little bubbles all in my tanks but thats where I am considering going with my problems because I have heard people saying it works well and is more consistant...... good luck to you
     
  4. banderbe

    banderbe Prolific Poster

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    Re: I can't get CO2 concentrations high enough

    My water's surface looks like glass. And no, I cannot see any bubbles. I could on my last reactor at anything over 1.5 bps so I built this new larger diameter reactor. Also no I have no ttried any other methods. The venturi reactor seems rather obtrusive.
     
  5. DaveMill

    DaveMill Junior Poster

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    Re: I can't get CO2 concentrations high enough

    Banderbe,

    Here are the facts as I see them:

    Untreated, your water is GH 22 KH 18, which is very hard. You inject 3 bubbles per second of CO2, and your pH goes to 6.8, which yields a CO2 level of 85ppm. If you back off to Tom Barr's suggestion of one bubble every three seconds of CO2, your pH goes to 7.2, which yields a CO2 level of 34ppm.

    What is the problem? It sounds like if you stick with one bubble every three seconds, you have the perfect CO2 level (Tom Barr's recommendation was a good one, as usual.) Then start looking at the rest of your nutrients.
     
  6. Tom Barr

    Tom Barr Founder
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    Re: I can't get CO2 concentrations high enough

    I add about 1 bubble every 3 seconds on a 20 gal high light.

    You might try using a limewood stone and the mist method.
    Cheap, unobtrusive, simple.

    Recall, I built CO2 reactors and sold them for sometime.
    Both internal and external.

    Now I generally suggest mist methods.
    Why?

    red 20.jpg
     
  7. banderbe

    banderbe Prolific Poster

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    Re: I can't get CO2 concentrations high enough

    The problem for me is that my ph test kit is clearly wrong, and based on all my observations my CO2 level is probably lower than I would otherwise think based purely on test kits and the kh/ph/co2 formula.
     
  8. banderbe

    banderbe Prolific Poster

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    Re: I can't get CO2 concentrations high enough

    Does that mean millions of tiny bubbles flying around the tank?
     
  9. Tom Barr

    Tom Barr Founder
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    Re: I can't get CO2 concentrations high enough

    Maybe hundreds, but not millions:)
    They are small also, much like pearling.
    If you don't like pearling, you will not like this method.
    But if you like pearling, great plant growth, easy to use method, no algae.
    It might be for you........

    You can see the above image. Not too many bubbles in that pic?

    Regards,
    Tom Barr
     
  10. PeterGwee

    PeterGwee Lifetime Charter Member
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    Re: I can't get CO2 concentrations high enough

    Pic is way too small to see bubbles....fine mist. :D

    Regards
    Peter Gwee
     
  11. banderbe

    banderbe Prolific Poster

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    Re: I can't get CO2 concentrations high enough

    What about noise? Does the venturi design you advocate make noise?
     
  12. colonel

    colonel Guru Class Expert

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    Re: I can't get CO2 concentrations high enough

    When I had one going inside my tank it did make a bit of noise, I mean not to much at all since it is inside the tank and all. But you can hear the bubbles being churned around inside of it faintly, and when the venturi kicks in you can hear the blades of the power head chop up the bubbles if your venturi line leads into the intake of the power head. Really its not bad at all though, just faint sounds here and there.
    Im currently trying the mist method.... which might be a better way to go if the tank is in a bed room or something, no noise but same mist effect, plus you dont have the reactor in the tank, just an air line and air stone.
     
  13. Tom Barr

    Tom Barr Founder
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    Re: I can't get CO2 concentrations high enough

    Noise: it does not make much, it's hard to hear and since.............I suggest turning off CO2 at night, you can still sleep even if it's right next to your bed.

    You can also minimize the noise to near silence: Ratgher than bubble the larger bubbles into the impeller, use a limewood stone into the suction side so that tiny mist bubbles are only taken in, these will not make noise and be chopped up much.

    But.........you may as well use a mist method at that point since that is what you are doing essentially. All you do is now remove the powerhead and place the limewood stone under the out flow of the filter and use a solenoid to turn the gas off at night.

    Simple.

    Regards,
    Tom Barr
     
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