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Understanding what is in the CO2 reactor...

Discussion in 'CO2 Enrichment' started by adechazal, Feb 15, 2011.

  1. adechazal

    adechazal Prolific Poster

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    Folks,

    I run an AM1000 reactor on my 180g. There is a vent tube recirculating excess gas back to the input of a Maxijet 1200 powerhead which handles the pumping duties for the CO2 circuit. Over the course of the day the reactor fills with gas to the point that it is completely empty of water except what is flowing through. Here's the part I don't get... If I purge all of the gas by opening the vent line to the atmosphere and refill the reactor with water, then reconnect the vent to the powerhead intake and really crank open the CO2 needle valve and re-fill the reactor with CO2 as it was before the purge, then dial the CO2 back to standard delivery BPS, the reactor almost immediately (20 seconds or so) fills back up with water???

    So I'm left with some possible conclusions on which I need input:
    1. The gas building up in the CO2 reactor over the course of the day is not CO2 but something else that does not readily dissolve in water. In effect it's a waste of time for me to recirculate this gas back into the reactor.
    2. After observing how quickly the reactor re-fills with water after purging the suspected "non-CO2 gas" can I say that a reactor full of true CO2 gas will dissolve in water within 20 seconds or so?

    Thoughts?
     
  2. Biollante

    Biollante Lifetime Charter Member
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    Hope Everyone Had A Great Arizona Day Yesterday

    Hi,

    I disagree with conclusions 1a and 1b, Conclusion 2 could be true but I am not sure I understand the relevance.:confused:

    {Full disclosure: I do not use or own the AM1000 reactor.}

    It seems to me you are simply running too much CO2 into the reactor during the course of the day.

    Assuming you are using CO2 of reasonable quality-

    • There is simply more CO2 than can enter solution.
    • Recirculating un-dissolved CO2 back is one of the better ways of preventing waste, somewhere after not using more gas than can enter solution.

    CO2 gas can and does dissolve readily in water.:)

    Biollante
     
  3. pepetj

    pepetj Lifetime Members
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  4. Tom Barr

    Tom Barr Founder
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    If you add an air line to the gas purge valve on the reactor, then loop this back into the pump's suction side intake before the reactor, this will atomize the gas as it builds up inside the reactor before it builds up.
    This ends up purging the gas out without wasting CO2.
    Simple solution to the issue.
     
  5. adechazal

    adechazal Prolific Poster

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    Thanks guys,

    I didn't mention it in my original post but indeed my purge line is routed back into the intake of the powerhead impeller. So I am chopping up the CO2 and still getting a buildup over the course of the day.

    From my research on this site regarding the AM1000 I believe it is a bit undersized for a 180g aquarium. So if I go to a DIY reactor from say Rex or similar, the reactor is longer but I presume I'll still get the buildup if nothing else changes.

    One thing I am researching now is the pressure inside the reactor. Some have suggested that if the setup allows a negative, or only minor positive pressure in the reactor, the amount of CO2 the reactor can process will be less than optimal. My CO2 water output line sits within the intake pipe of my sump return pump, I suspect it's possible that this setup is causing a suction on the CO2 water output pipe thereby reducing the pressure within the reactor chamber. Further, my reactor is mounted higher than the sump from which it takes and returns its water, i.e. when I turn off the CO2 powerhead and gas supply, then open the purge line to atmosphere, the reactor drains and pulls air in through the purge line. I suspect the best way to deal with these two "negative pressure" causes is to add a throttling valve on the output side of the reactor.
     
  6. pat w

    pat w Member

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    Or you could have a leak allowing room air to be sucked in. If that were the case you'd get a buildup of mostly Nitrogen which doesn't disolve well.

    Pat
     
  7. scottward

    scottward Guru Class Expert

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    Needless to say, although I'll say it anway, this is a very bad situtation to be in. Even if the AM1000 isn't completely full of gas as in your case, just a few inches could be too much, you'll run into trouble if you have a powercut. If you have a powercut, there is a good chance this gas will find it's way up into the impellor chamber of your pump. When the power comes back on, you will have a pump that is running dry (as far as I'm aware most pumps don't self prime). A dry run pump is not good. I know from experience as this happened to me, but fortunately I was home at the time and could here the pump chugging away with very little water. I was able to switch it off before it overheated and seized up.

    Using the dual venturi method, as Tom mentioned earlier, works great as long as you stay within reasonable limits. If you overwhelm the pump with CO2, the dual venturi loop still won't be enough to purge the gas, and you'll end up with an air space at the top (which again could cause a dry run pump).

    Personally I purge any build up gas from the AM1000 to a completely seperate needle wheel pump connected to a spray bar. That way I'm not wasting the CO2 and never have any risk of dry running my pump though CO2 build up.

    Just a quick thought regarding the CO2 dissolving in 20 seconds - I'm struggling to see how this is possible given that the water in the tank, at the time you performed the test, would have already contained a reasonable amount of CO2? Even if the water had very little CO2, it suprises me that an entrire AM1000 full of pure CO2 would dissolve that quickly?? Are you sure you had the air bleed valve closed properly?

    Scott.

    Edit: I just realised that you are using a powerhead, not an external pump. So I guess any dry run issues won't affect you. Nevertheless, anybody reading this who is using an external pump to power the AM1000, as is more often the case, take note!
     
    #7 scottward, Feb 23, 2011
    Last edited by a moderator: Feb 23, 2011
  8. Tom Barr

    Tom Barr Founder
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    In some respects it does not matter what type of gas it is or is not...........only that it gets purged and then fresh CO2 is added.
     
  9. scottward

    scottward Guru Class Expert

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    BTW Tom (and gurus), I understand that it is 'harder' for CO2 to dissolve as the CO2 concentration of the solute (i.e. the aquarium water) rises, but how much 'harder' does it actually get within the range 0 - 30 that we work with? Perhaps this (small?) range doesn't make a great deal of difference?

    So lets say a reactor that is completely full of CO2 (and let's say we put it there ourselves so we know for certain that it is CO2) suddenly has the water pump turned on and within 20 seconds the reactor is full of water again as the CO2 dissolves (bypass line closed so that the CO2 actually does have to dissolve in the reactor and cannot be flushed out). Let's say that it does this with aquarium water that has a low CO2 concentration, perhaps averaging 3-4ppm.

    If we conduct the exact same experient with water that is charged to 30ppm, would we notice a difference? Would the CO2 noticeably take longer to dissolve inside the reactor or would we only notice this if the water were some 100ppm+ in concentration?

    Perhaps the 0-30ppm band is so narrow that changes in CO2 solubility don't have any impact for our hobby?

    Scott.
     
  10. pat w

    pat w Member

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    Scott, I'm working on a different approach that may answer that question. I'm in the process of building a prototype of a reactor that forces as much CO2 into solution as possible with a Maxijet 1200 running in a ~ 6L closed loop. I'll be feeding CO2 at std. pressure in incriments of ~150ml via a float switch attached to the CO2 solenoid. The resultant mixture will be metered into the tank using a Dwyer rotometrer. I'm hoping to get 100ppm concentrations or better so we'll see.

    DIY Thread on APE
    Pat
     
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