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high kh and co2 absorption

Discussion in 'CO2 Enrichment' started by ibnozn, May 20, 2009.

  1. ibnozn

    ibnozn Subscriber

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    Is there a kh level I'd want to stay below in a planted Tanganyikan tank? I've read that higher kh requires more co2. I don't recall whether it either doesn't dissolve as readily or becomes less available to the plants somehow or exactly why this is. My tank has a buffering substrate so adding co2 causes the kh to rise gradually during the week about 3 or 4 degrees before it's reset back down with a water change. I switched back to tap recently so my kh is now running higher between 12dkh and 16dkh+ whereas with RO it was 8/9 to 12dkh during the course of a week.

    At the moment my tank is right around 16dkh. Ph is 6.7. My indicator is bright yellow and my fish are getting that wtf? look. I use both a Co2 reactor on the intake and an inline diffuser so there is Co2 in the water for sure. It's a 20 gallon using 3+ bubbles per second and I'm sure the circulation is fine. Ferts are 30N/3P using EI. My water starts to get a bit milky in the afternoon and I get a little pearling but nothing spectacular. It's high light - 70W MH but it's 12.5" above the water.

    I do get good growth from my plants and my algae has been receding. I'm worried about my fish though. Are my kh levels too high causing me to need more gas than my fish can handle?
     
  2. Philosophos

    Philosophos Lifetime Charter Member
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    Are those LTK cichlid planted tank compatible?

    What do you mean by a, "wtf?" look? Are they gasping or hanging around the surface, breathing rapidly? Any change in gill color?

    At 16KH and 6.7pH, and a solid yellow drop checker I think your CO2 could go down a bit if your fish are stressing; acidosis might be a concern at that level. Note that you've got to do this gently, keep a careful eye out for algae; it may creep in if you go too low.

    I think the milkiness may be from precipitation due to the high KH.

    The relation between CO2 and KH on charts isn't a requirement, it's a calculation method to find the amount of CO2. Altering your KH will not alter your CO2 levels. I don't know why plants would require more CO2 because of high KH.

    To be very honest, I don't know anyone who has done a plant-heavy LTK tank. The most I've seen is a mowed patch of vallisenaria, or some floating riccia. There's a general compatibility issue between fish and plants with the larger species.

    -Phlosophos
     
  3. Tom Barr

    Tom Barr Founder
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    Try this thought question:

    Does tap water sitting at the table for the last 24-48 hours with a KH of 2 and another with water with a KH of 10 have the same CO2 ppm?

    Of course..........

    Why?

    Why would this be any different if you add 3 bubbles a second of CO2 to either glass, would they be different in terms of ppm?

    They hold the same amount because they are enriched with the volume of additional CO2.

    They also hold the same amount because they have the same PARTIAL PRESSURE, this is how a CO2 meter probe works, it's independent of pH and KH.............

    Same for the tap water in a glass example, they hold the same ppm because the air has the same partial pressure of the CO2 gas.

    Bicarbonate can be used as an additional source of carbon, but it cost the plant and many species cannot use it also, so the total dissolved inorganic carbon is higher in the higher KH, but that's it.

    We enriched with CO2 so they do not use that source.

    Regards,
    Tom Barr
     
  4. ibnozn

    ibnozn Subscriber

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    Thanks for the answers. I think I figured out what was happening. The high KH was causing a ferric precipitate from my micros. I don't measure my iron levels but my plants were showing signs of iron deficiency so I recently upped my CSM+B liquid dosage from 2.5ml to 5ml daily. It coincides with the increase in this iron carbonate precipitation–milkiness that I've been seeing. It's always been an issue but I did a water change that lowered the kh and didn't dose micros yesterday and there was no milkiness. I saw more pearling too.

    Philosophos, Planted Tanganyikan tanks are certainly possible with the right plants. I currently have crypts, Rotala indica, java fern, java moss, hairgrass, H. micranthemoides and hc. Some plants fare better in high ph tanks than others of course but I don't think most Tanganyikan cichlids will tear up plants the way Malawi Mbuna can, it's more that they dig. I keep shelldwellers which are micropredators. They dig like crazy but I keep their shells in an area with sand that is separate from my plants so they don't uproot very much. I just started seeing fry recently so it seems to be working well.

    Tom, we've speculated it was low Co2 but since this seems to be the cause instead I've seen you recommend TMG over CSM+B as a possible fix for this type of milkiness. I'm going to keep the kh below 12-13dkh going forward but would switching to TMG help me any?
     
  5. Tom Barr

    Tom Barr Founder
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    Try adding Fe DTPA to the CMS mix since you have high KH.

    This should help as it's more specific to that KH than ETDA which CMS is.
    That should make the issue mellower for you.

    Add 1 teaspoon of Fe DTPA per 1 tables spoon of CMS. I know Alan sells it(aquariumfertilizers.com).


    Regards,
    Tom Barr
     
  6. wilsar

    wilsar Prolific Poster

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    Does tap water sitting at the table for the last 24-48 hours with a KH of 2 and another with water with a KH of 10 have the same CO2 ppm?

    Of course..........this is proven false by the Henderson-Hasselbach equation.

    The rise in pH that occurs when KH is added will be balanced to a degree by the dissolved CO2 in the water.
     
  7. VaughnH

    VaughnH Lifetime Charter Member
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    Could you elaborate a little on this? I don't understand it.
     
  8. Tom Barr

    Tom Barr Founder
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    Wilsar:

    I think this issue has been addressed:

    http://www.barrreport.com/co2-aquatic-plant-fertilization/4381-co2-solubility-function-kh.html

    For our purposes, this is true in theory, but not a significant issue in reality.
    I think the issue between high vs low KH and CO2 is overblown by some. For plants, they like a certain KH, much like fish(soft and hard KH's), but plants want CO2, not KH/HCO3.

    Some seem to like higher KH, some lower KH's, most hard water plants will do fine in low KH.

    Given a preference, I like lower KH water, but I have had little issues in harder water as well. Except in terms of KH and response of plants/fish and then only some species, the issue with CO2 is really a non issue.
    It makes virtually no difference in terms of CO2 in practical or in the theory over the ranges we use.

    Still, using partial pressure of gases, there's difference is pretty much the same.
    Partial pressure - Wikipedia, the free encyclopedia

    Henry's law assumes ideal gas, and that the gas does not react with the solvent (the water, which CO2 does with KH in the water and other salts, but not to large degree in our case say 20ppm alk vs 170ppm alk).

    An interesting issue with this:
    News Release - Increasing carbon dioxide and decreasing oxygen in the oceans will make it harder for deep-sea animals to "breathe"



    Regards,
    Tom Barr
     
  9. mi5haha

    mi5haha Prolific Poster

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    I try to maintain a reasonable KH for fish and shrimp when using RO water (mixed with hard tap water) with strong Co2 injection. pH value will quickly drop let's say from 6.8 to 6.0 if the injection speed is high in a few hours.

    Even targeting at GH6, KH3 when mixing RO water and hard tap water, KH in tank is still dropping to 0-1. Don't know why.

    The shrimps we get are used to hard water where they are caught, and many of them cannot survive when pH value is lower than 6.5. Many of them turn to blue color and lying on their back.

    So, trying to maintain KH to prevent pH drop, on the other hand, do not want to slow down the Co2 injection, that makes us to measure KH again and again when witnessing quick pH value drop. If KH is 0, or 1, I cannot maintain a quick injection speed while keeping pH from dropping. Either I have to slow down the injection speed to prevent shrimps from dying (water is too acid to them), and slow Co2 injection is not good for plants, or I have to raise KH to buffer pH value down.

    The concern here is mainly for shrimps, not for the plants. But KH to us is still a concern.
     
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