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What effect do carbonate using plants like val have on chemistry?

Discussion in 'Non-CO2 Methods' started by pusdesris, Jun 25, 2013.

  1. pusdesris

    pusdesris Prolific Poster

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    I assume:
    Code:
    (CO[SUB]3[/SUB])[SUP]2-[/SUP] + H[SUB]2[/SUB]O -> C[SUB]x[/SUB]H[SUB]x[/SUB] + O[SUB]2[/SUB]
    but does this tip the net ions toward positive, reducing the ph?
     
    #1 pusdesris, Jun 25, 2013
    Last edited by a moderator: Jun 25, 2013
  2. Tom Barr

    Tom Barr Founder
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    It'll reduce the KH, but the pH will actually go up.

    Because they remove the CO2, which causes the pH to move up, and then...they go after the remainder, the KH, same deal in tide pools and small ponds.

    Plants/algae suck up all the CO2, only then, do they start after the KH(HCO3).
    If there's no CO2 around(or not much), then being able to use HCO3 is a good advantage.
     
  3. pusdesris

    pusdesris Prolific Poster

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    I am afraid I don't understand. If the CO2 is effectively 0, will the ph still go up? What is the (simplified?) chemical formula to represent this?
     
  4. Tom Barr

    Tom Barr Founder
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    CO2 is not zero unless the plants/algae removed it.

    You have a ratio/proportion of an acid (CO2 in this case, and tiny fraction of which is H2CO3 1:400) and a base(HCO3 for our purposes).

    If you remove the acid by plant uptake, the pH will go up because only the base is left.
    It's a bit like a seesaw with 2 people on it, if you remove one of them, the end of the seesaw shoots up.

    Ranges for vernal pools: pH 6 in the early AM, up to 9-10 pH late in the afternoon.
    Tide pools along the CA coast; 8 right after the tide recedes, and about 10 right before the next tide comes in during the daylight hour tide changes.
    HCO3 is the same in both cases, but only the acid, CO2, is removed.

    If you do not add CO2 to a planted tank, the ph does not go down, it goes up during the light cycles.
    Try it and see.
     
  5. pusdesris

    pusdesris Prolific Poster

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    Perhaps I misunderstood my own premise. Val can absorb HCO3, correct?

    I get the H2CO3 and CO2 part. What I don't understand is HCO3 over the long run, as this presumably can be "used up" and doesn't vary throughout the day or get replaced by the air.

    As the HCO3 gets used over time, say a small percent every day after the plants run out of CO2, will the average ph gradually go down over the course of weeks? I don't mean the instantaneous ph at any time of day.
     
  6. Tom Barr

    Tom Barr Founder
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    There's evidence that Vals will use Bicarbonate as a source for carbon.
    Generally it's done by adding a lot of H+'s from the leaf which reduces the pH a great deal(say from 8 to 4) and this causes the HCO3=> CO2 which the plant then takes in.
    Indirect bicarbonate use.

    Yes, plants will soften and remove the KH over time if they use the KH as a source of carbon.
    Non CO2 tanks often start off with higher KH's, and end up with hardly any.
    Since few if any water changes are done on non CO2 tanks, the KH is consumed and not replaced via water changes, a little is for evaporation, but not much.

    At that point, the plants have only one source of carbon: CO2. Same occurs in small densely planted ponds and pools, backwaters etc.

    So yes, the average pH goes down, but it's better to think about the KH or alkalinity going down(this does not vary diurnally).
    pH will vary day to day, the KH will be more stable.

    If you add CO2, then the plants do not use the KH, and the KH stays the same.
    pH goes down when we add the CO2 gas, but the gas, not the pH, is really what this is all about and what the plants actually want, we can have high KH and add lots of CO2, vs say very low KH and not much cO2, and have the same pH's..........and the plants will do much better in the high KH/CO2 rich system.
     
  7. pusdesris

    pusdesris Prolific Poster

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    This is precisely the information I was looking for. I have a non-CO2 system and very hard water out of my tap. So water changes should promote better growth whenever the Kh gets too low. I know most non-CO2 systems don't really do water changes, but I think it makes sense to do them.

    I was talking to some other people in the area with non-CO2 tanks and noticed that their ph was sub 6 (even though the tap is 9) which didn't make sense to me. I had assumed it was plants absorbing bicarb or snails using it up to form shells.
     
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