too much CO2

Discussion in 'Carbon Dioxide (CO2)' started by sks, 22 Jan 2008.

  1. sks

    sks Guest

    Not something you would want to deliberately set out to do, but I have to ask: what happens when you put in too much CO2?

    For the last 2 days since the water change I have possibly over shoot my CO2 to get to a level where my drop checker is verging on yellow, not quite there, but almost there if you know what I mean. It wasn't uncomfortably enough for the fish to start acting stressed but I noted that pearling basically stopped. And this at high CO2!

    What I need to know is if this true, does having higher CO2 stop pearling somewhat? Either my drop checker is wrong or my dosing of the ferts is not enough. I ask because I saw what was happening today and turned the CO2 off for the level to recover and the plants started to slightly pearl again. I deduce it can't be lack of ferts since this has been constant all this time.
     
  2. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    Hi,
    Under normal circumstances, it's virtually impossible for aquatic plants to receive too much CO2. The current thinking is that because the absorption rate at the boundary layer (the leaf/water interface) is never as good as it would be if the plant was exposed to air. This is why the "misting" technique, which involves gaseous CO2 making contact with the leaf surface is now very popular.

    What is so bizarre is that from what I understand, there is a relationship between the CO2 uptake and Nitrate uptake such that increased CO2 drives additional NO3 uptake. The EI credo is to generate unlimited supply of every nutrient for the given light level, so it's conceivable that you would have needed more NO3 for the amount of CO2 you added.

    If the fish are not stressed there is no way I would actually lower the CO2 injection rate (but I'm a CO2 fanatic :rolleyes: ) - just add more of everything else (except light).

    It would be interesting to see what happens at the elevated CO2 level and additional ferts. Remember that yo-yoing the CO2 can bring the onset of BBA though, so hold the max level for a week or so and see what happens to growth.

    Also, I´m not sure I would use pearling as a barometer because there are so many other factors affecting pearling, like temperature etc.

    Cheers,
     
  3. Ray

    Ray Member

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    How does temperature effect pearling Clive?
    Cheers,
    Ray
     
  4. stevet

    stevet Member

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    hmmm...this whole pearling issues gives me food for thought. I was under the impression that pearling is also a function of how saturated your water already is with O2. That is to say that the act of photosynthesis causes the plant to give off O2 - if the water already has high O2 saturation (as mine does - i have a trickle style filter) then pearling will occurr earlier than in some other tanks? The mechanism being therefore that excess O2 produced by plants cannot be absorbed into already O2 rich water and therefore escapes in gaseous form, hence pearling?

    Therefore simply saying the addition of CO2 causes pearling could cause some confusion. Its true the addition of CO2 will aid plants in photosynthesis, but if your saturated O2 levels are low you may never see pearling as the water never reaches O2 saturation point. This does not mean the addition of CO2 is not aiding the photsynthesis process - it is.

    Temperature plays a factor as the O2 stauration point is aligned to the water temp. The O2 saturation point of warm water is lower than that of cold. I would imagine therefore following my logic above a tank at 32C MAY pearl earlier than one at 26C?
     
  5. sks

    sks Guest

    Clive,

    a few points:

    1) would not the misting diffusers be impractical over a large aquarium? simply because CO2 is so apt to dissolve quickly so either you need immensely strong current to blast it around to cover everything or else it's dissolved too quickly at it's gaseous state to reach the areas you want. Of course there's nothing stopping you having multiple diffusers around the tank but that involves added complexity of splitting the CO2 line and the regulatory issues involved.

    2) I'm dosing JamesC PMDD, so the ratio of the ferts are fixed. Taking your comments into account I've decided to lower the CO2 slightly. I've also decided to add KNO3 as well to supplement the dosing. I've noticed at high CO2 the fish are more docile, 0.2 pH higher (pH 6.7 on my controller, although I suspect my probe might be going) they're more "active" with the clown loaches going up and down the glass and being more playful.

    3) The only algae I have is GSA on the glass and what appears to be some kind of thread algae on the tennelus and starting to appear on the Blyxa, but this is on old leaves.

    4) I am beginning to suspect that my Cabomba are hogging all the ferts. Does it not stand to reason that since there are so many different plant species some are just so much more able to process/take up ferts better than others, and the dosing regimes are meant to be adjusted for different setups and species. I suppose the only way for me to know if I am dosing right would be to calibrate my test kits and measure the values

    5) I've always wanted pearling, and I find it puzzling that sometimes it happens and sometimes it doesn't. If it's not a particularly good barometer why do we mention is so much here and there?
     
  6. JamesC

    JamesC Member

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    The water doesn't have to be saturated with O2 for pearling to occur. Pearling will occur if the rate of O2 production is greater than rate rate of O2 absorption in the water. The rate of O2 absorption will be affected by certain parameters including temperature and O2 saturation. The higher the temperature the less soluble the O2 is so pearling will be greater. Similar to O2 saturation in the water, the higher the level of O2 in the water the slower it will dissolve and the greater the pearling will be.

    Increasing the CO2 levels may also have led to an increased use of other nutrients, namely NO3. This may have actually led to NO3 being limited and so slowed plant growth and pearling even though CO2 is high. I've run CO2 really high in a tank with no livestock and plants do fine.

    James
     
  7. JamesC

    JamesC Member

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    I'll jump in if I may.

    Yes, diffusers in large tanks are problematic due to, as you've said, getting the CO2 distributed around the tank. On a four foot tank with very good flow you can get away with one, but if your tank is bigger you'd need two.

    High CO2 will make the fish more docile as they will be out of breath so to speak. Some fish are more affected than others. You have to be sure that O2 levels are good by agitating the surface and keeping the surface scum free. The PMDD solution I use works differently to Estimative Index in that PO4 is limiting and so controls plant growth. This means that CO2 does not need to be so high as plant growth is slower. Just needs to be stable.

    Your tank is new so algae is quite likely to appear. I get it as well on new setups but now just leave it alone and it always just goes by itself in a few weeks. Stability and heavy planting I think is the key.

    Some plants do use more ferts than others, but it shouldn't cause a problem. My tank is full of hungry fast growing stem plants and 4WPG but the slow growers do fine as well. I do use test kits on odd occasions but don't reall pay too much attention to the results. More of an indication really. It's a lot of hassle to make solutions and calibrate.

    If you want pearling then dose Estimative Index. The PMDD solution I use is designed to slow plant growth down and so you get less pearling.

    HTH
    James
     
  8. stevet

    stevet Member

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    I've been labouring under a misconception about this then - this is discussed in the barrreport forum in greater detail. Tom feels mine is a common mistake made. He goes on to discuss other technicalities like O2's relative insolubility in water etc.
     
  9. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    Hi,
    As can be seen in James' explanation there are some physical idiosyncrasies to pearling that makes it a less than ideal indicator. Ultimately plant growth is the better indicator. The general idea is to learn to see and read your plants better, simply by close observation.

    On sks point 1 - Agree with James that misting is problematic in big tanks. I've gone the route of inline diffusers - but this has to be accompanied by much higher flow in a big tank.

    On point 2, as stated, PMDD uses PO4 as a limiter while I suppose EI would use light as a a limiter. Lower light lowers demand for everything else so growth slows.

    On point 3, yep, fundamentally agree.

    On point 4, It's unlikely one group of plants can hog with distribution presented by the filter output. Hygrophilla uptakes more quickly than say, anubias but if you are dosing regularly there is no way on plant can prevent the other from uptaking.

    EI extremists like myself don't even know how to spell test kit. Remember that the tank as a whole can only consume X ppm amount of nutrients per day. "X" rises as a function of light intensity. As long as you dose higher than this value "X" you ensure that Cabomba cannot take the candy from the mouth of anubias :lol: This simple arithmetic means that I never need to test.

    Hope this helps to clarify.

    Cheers,
     
  10. sks

    sks Guest

    well due to my slight rashness today I not only added more KNO3 but add 1.5 times more PMDD solution too. The result was that nearing the end of the light period pearling kicked in.

    I see what you are saying about pearling, it's not vital that I have it and having it does not necessarily mean that conditions are optimal.

    Clive, your inline diffusers, are they close to the tank or far away? I ask because if the point of diffusion is some length away wouldn't the CO2 dissolve on their journey to the tank? I mean if CO2 is already dissolved by the time it reaches the tank you effectively have a CO2 reactor and not a CO2 diffuser.
     
  11. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    That's it mate, you've got it! There is no denying that a curtain of bubbles is lovely to see, and is never a bad thing as long as we don't become mesmerized by the bubbles and make them more important than they really are.

    Well to tell you the truth I'm never really sure what the differences are between the two. There is a half meter of tubing between each unit and the tank. I use two different types, one of them is here and is called a diffuser: http://www.aquaessentials.co.uk/index.p ... ts_id=1370

    The other is called the Aquamedic 1000 Reactor. In each unit, by the time the flow reaches the spraybars the bubbles have disappeared. In the case of the diffuser, I can see the mist rising from the porous stone. In the case of the reactor there is a counter flow as the bubbles rise against the water. I can't see any real difference between the two in practical terms except perhaps that the Aquamedic is 7 times bigger and perhaps has a higher capacity.:rolleyes: I do notice that the Aquamedic has a higher back pressure so that the filter that it is attached to has a lower output flow (I don't like that bit at all).

    Cheers,
     
  12. sks

    sks Guest

    From the looks of it the Cal Inline diffuser is making a low pressure spot and introducing it there, so this creates a sucking effect, with no back pressure. The aqua medic will create back pressure because you are going against the pressure of the flow, like two forces colliding.

    I have the aqua medic as well but it's not used. I have a Dupla one that works on exactly the same principle but the unit is not as nice as the aqua medic's.

    What I'm getting at is if both give water without bubbles at the other end they are doing the same thing. I'm sure you can up the flow of the Cal diffuser without any negative effects as long as the glass can take the flow, and this flow might be fast enough for you to see bubbles coming out the other end, creating the misting that you want.
     
  13. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    Well, I tell you what's really weird. I've got two of those Cal diffusers (only use one at a time - swap out for cleaning) one of them only seems to allow a much slower bubble rate, while the other allows a much faster bubble rate. Now this is with the exact same settings on the needle valve. The two look identical. I split the CO2 from the regulator and send one line to the Aquamedic and the other to the Cal. If I have the slow one mounted, the Aquamedic gets a whopping flow. If I have the fast one mounted the Aquamedic get almost zero flow. I'm unable to determine what is causing the apparent back pressure in the slow one and why the fast one has such wide open gas flow. I swear they look identical. Maybe small differences in the gap that allows the water to bypass? Bizarre.

    Cheers,
     
  14. sks

    sks Guest

    I'd trying blowing into the Cal diffusers to see if there is a difference of resistance between them. What it seems like is that you have a differentce in resistance, but I suppose that's to be expect for something hand made (I believe the Cal diffusers are, aren't they), and their diffusion plate might not be as uniform. Also their shape and placement of the diffusion plate will effect their workings.

    If I were to split my CO2 into two reactors that go into the tank I'd always make sure that both reactors have the bubbles exit at the SAME depth or else you run into pressure differential problems. Gases also follow the path of least resistance. :D

    In your case I would be inclined to fit inline speed regulators (these are basically needle valve's aren't they?) for each CO2 output since this lets you adjust to compensate for the differential pressure requirement. On second thoughts you can just get away with one inline speed control in the higher resistant unit because you know where the rest will go.
     
  15. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    Well they sure have a hand made price, that's for sure. :arghh: It's a pity there is nothing to adjust on the unit.

    Yes I agree about the exit depth. As far as practicable I have them within centimeters of the same depth.

    I thought about the CO2 output control but it would be yet another thing to possibly leak... Actually, after a few days the fast unit gets clogged with a bit of algae and it slows down, then the CO2 flow evens out :rolleyes:

    Cheers,
     

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