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Definition of Good CO2

Discussion in 'Talk to Tom Barr' started by AquaticJim, Aug 26, 2007.

  1. AquaticJim

    AquaticJim Guru Class Expert

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    Hi Tom,

    I have read the term "good CO2" lots and lots of times, but it doesn't really mean anything to me. Could you please describe and enlarge on what the definition of good CO2 is and how to achieve it. I'm new to CO2, learning, but still new. And like all things new, sometimes they can seem over complicated and a higher hurdle imagined than what in fact it actually is. An explanation of the term good CO2 will assist me and I'm sure many others.
     
  2. VaughnH

    VaughnH Lifetime Charter Member
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    "Good CO2" is, above all else, the same concentration of CO2 in the water every day during the lights on period. It doesn't need to be that level when the lights are off, but it should be at that level as soon as the lights come on in the morning.

    Next, the amount of CO2 in the water should be near 30 ppm for very high light tanks, or 20 ppm or so, for lower light tanks. And, these numbers should be determined by using a drop checker with known KH distilled or DI water to be reasonably sure of the accuracy.
     
  3. AquaticJim

    AquaticJim Guru Class Expert

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    I'm just stumped at how people get their CO2 up to 30ppm as soon as lights go on. Are people switching their gas on hours before the light comes on or do they have super duper CO2 reactors and if thats the case, what stops the CO2 getting too high through the photo period especially towards the end?

    Also on water change day, if I do a 50% WC with aged tap water that is approx p.H 8.2 - 8.5 this brings the p.H up again. It still takes hours for the drop checker to indicate 30ppm again.

    I use a Dupla Reaktor 400 and 2 bubbles per second on a 400 litre aquarium.

    I know this might all be easy stuff for a seasoned hand at this, but its a steep learning curve and an answer leads to yet more questions.

    I thank you for your time.
     
  4. VaughnH

    VaughnH Lifetime Charter Member
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    Your aquarium is too big for only 2 bubbles per second. That would be about the right amount for a tank about half that size. I now keep my CO2 on all of the time, but at only about 15 ppm for the relatively low light I have - 1.6 watts per gallon. You can turn on the CO2 an hour early if necessary to give you a good chance to reach the desired amount of CO2 in the water when the lights come on. And, one of the best reactors for getting the CO2 level up quickly is an external, in-line reactor, which is extremely easy to make yourself and install in a canister filter return.

    When you do water changes you don't need to age the water at all. Just add Prime or another dechlorinator to the water in the tank as you add the new water. That way you start out with whatever CO2 is in the tap water, and that can be several parts per million. When you have some surface water circulation you don't have to worry about the CO2 building up continually throughout the day. You lose CO2 from the surface, which balances what you are adding. Then you just adjust the bubble rate until you get the right amount in the water and it should go back to that amount every day after the solenoid valve opens in the morning. You just have to play with the bubble rate, the tank water circulation, and the timing for starting the CO2 in the morning, until you get where you want to be. It can take awhile.

    There are other ways to add CO2 to the water, too, some of which are also pretty rapid acting.
     
  5. PeterGwee

    PeterGwee Lifetime Charter Member
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    Drop checkers have slow response time which is an issue by itself and cannot be used to judge your CO2 system response. A rough check with the pH drop method can be used to give you a rough idea whether your CO2 system is responsive enough or not.

    Regards,
    Peter Gwee
     
  6. Joetee

    Joetee Prolific Poster

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    With my drop checker, I get a fairly fast reading as I increase the c02 level, but if I lower the bubble rate real low to get the drop checker to start turning a little blue again, it does not decrease from yellow, to green, to blue even after 3 or 4 days. What I have to do is replace the fluid and start from blue again. Slowly increase my bubble rate until I get it back to green, very slowly making adjustments daily.
    Why won't it turn back to blue or green again after turning down the rate even after 3 days?
     
  7. VaughnH

    VaughnH Lifetime Charter Member
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    The CO2 concentration in the tank does not drop to zero just because you turn off the CO2. It will certainly drop, but how low and how fast depends on lots of things, from surface water disturbance to plant density to tank water circulation to tank size vs. surface area, etc.

    My drop checker reacts to both increases and decreases at about the same rate, about 2-3 hours to stabilize as close as I can judge the color.
     
  8. AquaticJim

    AquaticJim Guru Class Expert

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    Thanks to all who replied, great information.
     
  9. Tom Barr

    Tom Barr Founder
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    I'm not really sure what it means without context either:p
    I'm serious.

    Folks often just do not bother to put the other elements into context. I often make the mistake that they do, nope, not everyone, no way:D
    That includes my own self:rolleyes:
    So no one is immune.

    I'd say CO2 is the most controversial things in the hobby, kills more fish, causes more algae and generally can be a real PITA.

    I think it is rather hard to suggest a particular level of concentration without also considering light intensity.

    Problem is, there are no good hobby level ways of standardization for plants.
    Folks come up with all sorts of methods, equations, charts etc, all in effort to improve the watts/gallon rule, various light efficiencies differences etc, by the time you do all that, you are really just getting to a very rough estimate anyway.

    So relating light, which drives CO2 uptake(no way around this one), to a good CO2 ppm level is tough.

    And that does not even include plant biomass difference between tanks:)

    Ugh.

    So, what do I suggest here?
    A bit of two things, watch the plants and learn them well.
    And use good measurement methods.

    Plants are the ultimate "test".

    I manipulate things, get excellent plant growth, then ..............I go back and see what drives that growth, see what and why the plants did well under those conditions.

    Many assume that some pre concluded ppm or level is "best" and do not bother to define what is "best".

    It really depends one your goal.

    I know what level of CO2 ppm for at least dozen or so plants is maximum, at the highest or very high light, about 30ppm, but other species might grow better at 40ppm etc.

    Of course with low light, and non CO2 methods, 1-3ppm is fine, but you have slow growth and competition amongst species(and algae) for the little CO2.

    Simple question, not a simple answer.

    Regards,
    Tom Barr
     
  10. AquaticJim

    AquaticJim Guru Class Expert

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    Thanks for the reply
     

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