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Could anyone explain high CO2/low pH readings ?

Discussion in 'CO2 Enrichment' started by Nothingman, Mar 12, 2010.

  1. Nothingman

    Nothingman Junior Poster

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    The problem for me is that I can't measure CO2 correctly.
    Maybe someone could explain me why in my tap water I get ~7.2pH and ~13kH which gives about 25ppm of CO2 (in "normal" water I should get about 5ppm reading, as I read somewhere). If I leave water for a night, at best I get to 7.3pH which is also something quite wrong.
    Later it gets even better :) - in my aquarium in which I pump pressurized CO2 I get ph6.6-6.4, 13kH readings, which would state that I have 100-150ppm of CO2. Fish and Amano shrimp were feelling good, until I changed my CO2 reactor last night, I tested this morning after collecting dead bodies of amano and ancistrus, and it was about 6pH (actualy my test only shows as low as 6), so I have 400ppm of CO2 in my aquaria :D well it is getting kind a funny but how could I know how much CO2 should I pump... before killing fish? Would it be a correct approach to drop it by 1pH no matter what kH is ? lets say, if I have 7.2-7.3 in tap water, and serve enough CO2 to drop it until 6.2-6.3, then I should have aprox 25 or so ppm of CO2 ?
    I have two drop checkers in that aquarium, but they are always yellow-green, after I put my DC in aquarium I never see nor blue, nor darker shades of green again(I use 4kH water from local store and bromothymol blue or whatever it calls it self :) ), I leave air supply from internal filter all day long. I have been trying to supply 1bubble about every 1-10sec of CO2 and I still don't get dark DC colour (I left 1b/s for a while now because it seemed ridiculous for me to serve 1bubble in 10-30sec or so just to get dark green DC colouration at evening). How it could be, I think even without any plants serving that little should evaporate it to almost nothing, and I had hornwort and very big Hygrophyla Corymbosa not mentioning other plants (yesterday I restarted my aquarium... but this post is getting too long already). DC I think works fine, 'cause in my shrimp aquarium without CO2 I always have blue colour.

    In summary what would you suggest, should I adjust my CO2 servings by DC (even if it gets to 1bubble/30sec to read dark green in the evening)? adjust by pH/kH table, which in my case would mean almost no serving of CO2 at all? or should I just drop by ~1pH?
    Aquarium 112ltr (29g), light: 4x18W for 8hours
     
  2. shoggoth43

    shoggoth43 Lifetime Charter Member
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    The pH/kH table is only accurate for your aquarium if you have ONLY kH hardness in your water. In most cases people have GH too. You also have other acids and things in the water with your fish, so the results you'll have are going to vary widely. Where it IS accurate is in your drop checker. You should have a distilled water solution of 4KH, which it seems you do. There are a few threads on here about the drop checker never dropping back to blue which may help you a bit. It appears as though you never really blow off the CO2 fully at night. Unless you are heavily stocked, this wouldn't really concern me greatly other than as a sanity check. Move your DCs around a bit and see if they change, they may just be in a low current part of the aquarium. People have mentioned a biofilm building up on the water surface inside the DC which you may want to check on as well, this might be preventing the DC from outgassing the CO2 and preventing it from changing when it should.

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    S
     
  3. Nothingman

    Nothingman Junior Poster

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    Thanks shoggoth43,
    I didn't know that GH also influences the pH/kH table readings. The one question still remains is it worth to check CO2 by pH drop, or it aslo could be messed up by other elements in water ?
     
  4. shoggoth43

    shoggoth43 Lifetime Charter Member
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    I'm not really sure on the pH drop question. I would think it's still a possible variable since you don't know what might be going on in the water. In theory it should be fine so long as you get your sample back to atmospheric levels of CO2 vs. the extra amount you normally inject into the tank water. It's probably better to let some of the more expert types field this one.

    ( They'll hopefully correct any of my egregious errors in what I've told you to date as well. )

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    S
     
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