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Misting and co2 levels

Discussion in 'CO2 Enrichment' started by Henry Hatch, May 12, 2009.

  1. Henry Hatch

    Henry Hatch Guru Class Expert

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    The recommended level for co2 is 20 - 30 ppm. Many people, including me, have reported increased plant growth and vitality using co2 mist.

    However, co2 misting is lossy and it takes more co2 to achieve the same co2 level as with a reactor which dissolves most of the co2 into gas.

    Plants can use co2 more efficiently in a mist form. However, a drop checker will measure only dissolved gas and not the bubbles which plants can use more efficiently.

    Can I conclude that when using co2 mist I need a lower level of "measurable" co2 since the most usable form of co2 is not measurable ?
     
  2. shoggoth43

    shoggoth43 Lifetime Charter Member
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    That has been my experience. On the other hand, if you use enough CO2 mist to still get a drop checker in the green range you're definitely good to go. At the point the only issue you might have is poor flow in the tank.

    -
    S
     
  3. SuperColey1

    SuperColey1 Guru Class Expert

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    If your flow is adequate with misting then bubbles will enter the DC air gap just as dissolved will.

    I would go as far to say that bubbles will pass through much easier than dissolved because they hit the air gap and 'burst' rather than having to come out of solution.

    At least that is what happens with mine. Bubbles hit the opening just as they do the water surface where they stay for a while before 'bursting'.

    I don't think there would be much difference in loss really from reactor or misting if the flow is right. People seem to think that misting does because they can see the CO2 in the form of bubbles rising to the surface at some stage of their route around the tank. They forget that the CO2 in solution from a reactor also hits the surface at some point but because it is in solution they don't see it just as the CO2 that goes into solution while the bubble is getting smaller will.

    No idea how much difference )if any) there would be but it is always going to try to return to 'equilibrium' wether the CO2 is in bubble form or not.

    It is a similar argument to pearling. Some people panic because they don't get pearling but that just means that O saturation has not been reached. The plants are still releasing O but it is going into solution until a point is reached where the water can take no more and therefore the O forms in bubbles instead.

    Judging by the bps (I know bps is only indicitive of the quantity of CO2 being injected by the particular setup a user has) that some people with similar sized tanks and light as me use with reactors I would go as far as to say that I use less than them. this may be due to me having superior circulation or just a better balance but a 600g bottle lasts me almost double the time it would on theirs whilst still reaching green/lime on the DC and seeing pearling too.

    AC
     
  4. Tom Barr

    Tom Barr Founder
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    I think simply eyeballing the plants as a test kit of measureability might be better.

    I'm not a DC fan, I am a fan of a method that uses a reference, but it's still a long response time and color metric test.

    Adding a pH probe inside a Drop checker with the reference KH solution is much better, but still takes 2 hours or so................and is dependent on flow rates in/near the drop checker. If you use a drop checker, make sure to have it in an area of high flow.

    The way to measure the mist method is through plant growth, we can use O2 readings to do that, higher O2= more plant growth.

    Say you have 7ppm when the lights first come on(95% saturation) and you add CO2 with good light. Later after 8 hours, the O2 is now 8.5ppm (say 120% saturation). Now with CO2 mist, after hours, the O2 is now 9.6ppm (155% saturation).

    35% increase in O2 saturation.

    The rise was 1.5ppm of O2 in case one(no CO2 mist)
    With CO2 mist, the rise was 2.1ppm.

    pH/KH suggested the same reading for dissolved CO2 as did a CO2 meter(6 replicates).

    This would suggest more plant growth even with the same dissolved CO2.

    Now this may or may not be due to the theory behind the gas phase etc, or it might be a factor of the mist breakingt up boundary layers around the leaves and improvement of circulation, sticky surface tension pulling off epiphytic algae and dust making the exchange of CO2, access to light and nutrients much better.

    It has not been shown that it is the fact the gas phase causing the improved growth.

    There are a few methods that might better get at that question.
    But it's pretty clear the mist does improve health and growth of aquatic submersed plants. "Why" is still debatable.

    A control might be using aeration or N2 gas to mimic the mist while maintaining the CO2 dissolved ppm's, but unless you have a a very accurate way to measure CO2 dissolved and want to measure multiple spots quickly in a tank as the test occurs, you cannot do that.

    So you need a device like the CO2 meter, which is about 2000$.

    Regards,
    Tom Barr
     
  5. JDowns

    JDowns Lifetime Charter Member
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    I have to agree with this.

    If I place my drop checker anywhere in the tank I get a very slow response time, greater than 2 hours. If I place my drop checker in my overflow chamber, the boundry layer is actively moving, I get much faster response time, within an hour. I found moving my drop checker to a higher flow area registers less CO2 in the drop checker, since then I've increased CO2 significantly, and the results in growth are significant.

    The drop checker will register yellow in the tank in lower flow areas, in the overflow chamber more of a lime green. Quite a variation. Late in the evening the drop checker in the tank will never get past green, but in the overflow will get green/blue.

    As Tom has stated don't put to much faith in the drop checker. The plants should be your first indicator. If your having signs of CO2 deficiencies in your plants, but your drop checker is showing good coloration, which should you trust?
     
  6. Henry Hatch

    Henry Hatch Guru Class Expert

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    I use a drop checker with reference kh solution. However I've been putting it in areas of low flow deliberately thinking that would be the area of lowest co2 concentration. Evidently that is not the case. I am not clear on the concept of boundary layer which I have seen referred to a number of times.

    I agree that using your eyes is the best measure of how things are going in your tank. However, developing this skill is difficult and takes a lot of experience.

    I use a drop checker not so much to determine in absolute terms co2 levels, but to measure in relative terms the affect of taking certain actions to alter co2 levels.
     
  7. VaughnH

    VaughnH Lifetime Charter Member
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    Boundary layer: When a fluid flows past a surface, the fluid that is in contact with the surface will be barely moving, while the fluid farther from the surface will be moving at full speed. The layer of fluid that is moving slower than the full speed is the boundary layer. High velocity flows have thinner boundary layers than low velocity flows.

    Now you are a fluid dynamics expert!
     
  8. Tom Barr

    Tom Barr Founder
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    Point is, placement of the DC has a large variation tank to tank.

    Folks rely way too much on it.

    And ppm';s for test kits, pH/Kh for CO2 etc in general.............

    Even the 2000 meter has the same issues as a DC does with respect to placement.
    some spots have higher, some lower, 5-10X in some cases.

    Quite large.

    Regards,
    Tom Barr
     
  9. JDowns

    JDowns Lifetime Charter Member
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    I agree that is where it is usefull, along with once your system is dialed in and plants are happy, it can be a quick glance indicator that things are what they were yesterday. Where it fails is when a person relys on it as an absolute truth. I've seen more than once, and in my own experiences as well, the thought process of; My drop checker is yellow so it can't be CO2. Even though the plants deficiency and/or algae issues clearly point to lack of CO2.
     
  10. Tom Barr

    Tom Barr Founder
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    then they yell at me for suggesting it's CO2...........and then blame NO3 or PO4, or some weird interaction between some obscure terrestrial reference they cooked up off the web somewhere in desperation.........

    Probably had 20 or more such bouts:cool:

    I often wonder if they figured it out later or are they still stuck in that rut.
    Few come back and say the truth after they drew such a big line in the sand and claimed they must be right and I must be wrong.

    But that is exactly and mind set that goes on.

    CO2 is one of those things that really messes with folks in this hobby, there's no doubt. It's the number 1# killer of fish, the no#1 algae inducing issue, but they still focus on nutrients.............very often ignoring light intensity as well.

    I suppose that is why I never have any issues due to nutrients........;)

    Regards,
    Tom Barr
     
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