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Co2/ph/kh Table

Measure your KH, then see how much you need to reduce the pH to get your target CO2 ppm.
  1. Tom Barr

    Tom Barr Founder
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    Please ignore the recommended ranges for good/Bad CO2 ppm, they vary by tank and lighting and other factors, a good range to target initially is 30-40 ppm.
    Then adjust slowly watching plant health and vigor.

    CO2_Graph_zps9c124ef0.gif
     
  2. Tom Barr

    Tom Barr Founder
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    Measured your KH, then see how much you need to reduce the pH to get your target CO2 ppm.

    Say you tap water is a KH of 5m say you want 35-40ppm of CO2, you should add enough to get the pH to 6.6 and be able to keep it there.

    Warning, KH may not be entirely carbonate hardness. This means you will think and believe you have MORE than you actually do, thus you may be under dosing CO2.
    This issues will never be the reverse, eg, you are adding more CO2 than you think.

    So the error is always on the safe side usign this method.

    As the KH in your tap drops, say your KH is 1-2 degrees, there's just not much room for other sources of KH other than carbonate, at 4-5 and above, there may be.
    So assuming most of the KH is carbonate hardness for a KH or 1 degree is likely okay.

    Say you want a CO2 of 50 ppm for a KH of 1 degree? the chart does not cover those ranges of pH's, but you can scale using a similar higher KH to see what the pH adjustment would be.
    So about 5.9 pH would give about 39 ppm and a pH of 5.8 would give about 48 ppm of CO2.

    I typically use a pH meter, American marine works pretty good.
    Then a nice CO2 reg, check valve, needle valve etc to dial it in.

    I would say 1-2 bars into the red is ideal also in the above graph.

    Another good item to use for KH: Hanna alkalinity meter is pretty good IME, same with the Lamotte alkalinity test kit.
    Test tank water and tap water every month or two as a good measure. Over a season, KH can change from some Tap supplies.
    Mine goes from 1 to about 2 each season. About 19-20ppm to about 35-38ppm.
    So I'm in the 5.8-5.9's to 6 flat for pH's mostly.
     
  3. Vanderj

    Vanderj Junior Poster

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    Can my fish provide adequate CO2?

    I've recently began planting my 1 year old 46 gallon tropical tank. I have 15 fish currently and sufficient lighting. Is the adding of CO2 imperative for the healthy growth of my plants?

    Thanks!
     
  4. Darkblade48

    Darkblade48 Guru Class Expert

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    What is "sufficient" lighting, in your case? Depending on your lighting conditions, CO2 may be imperative for healthy plants. In lower light aquariums, while CO2 is not imperative, its addition will only benefit the plants.
     
  5. Tom Barr

    Tom Barr Founder
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    Most of the better scapers seem to eyeball cO2, they start with some relative measure of dosing for CO2, then they tweak and adjust slowly from there.

    I do the same thing with the pH/Kh chart, but not those charts above:)

    Also, as you depress the pH with CO2 gas, the concentration will increase a lot more(eg, it's non linear) for each 0.2 units of pH.

    Say you have a KH of 3 degrees.

    At a pH of 7.0 you would have 9 ppm
    At a pH of 6.8 you would have 14.3 ppm
    At a pH of 6.6 you would have 22.6 ppm
    At a pH of 6.4 you would have 35.8 ppm
    At a pH of 6.2 you would have 56.8 ppm
    At a pH of 6.0 you would have 90 ppm

    Differences between each 0.2 pH units:
    5.3 ppm
    8.3 ppm
    13.2 ppm
    21 ppm
    33.2

    So your pH measurement and observations need to be very good when you use more CO2. If you over do things at the higher ppm's, it only takes a little bit of change to dramatically increase the CO2.

    This is one reason why many people fail when adding more CO2 and gas their fish instead. If each 0.2 pH units were only 5 ppm difference, then it would be pretty easy to adjust CO2. This is also a good reason to buy a nice CO2 regulator, needle valve etc.

    Ah but what do I know, hehe:icon_mrgr

    Since many use the drop checkers and there's little differences between the colors and those color changes are at best, 0.2 pH, what does this say at the higher ppm's of CO2? Not much.

    Or if they use colormetric pH measure? Similar.
    A good 0.01 accuracy pH meter is likely the best relative measure for CO2 using pH.

    I knock my pH down about 1.4 pH units. This is about 47 ppm.
    If it went to 1.6, then I'm at 75 ppm's, if I back off just a hair, 0.1 pH units, then I'm about 1.5 pH units, I'm at 59 ppm. 1.3 pH units, 38ppm, 1.2 pH units, about 30 ppm.

    Tweaking CO2 is not some simple thing. It's not something to just wing it and assume the drop check has to be correct. You need to be careful.
    A good pH meter can help make small tweaks and adjustments.
     
  6. dutchy

    dutchy Plant Guru Team
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    How much of the KH may be non carbonate hardness and by what is this caused?

    What is the influence of driftwood on pH in relation to CO2?
     
  7. Tom Barr

    Tom Barr Founder
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    pH due to driftwood, tannins etc, can be easily removed with a large water change and/or with activated carbon.
    So that can be accounted for.

    As long as the rate of CO2 is stable, the post measured build up and depression of pH can be measured, then you can reset the pH again by keeping the CO2 stable, thus independent, and remove the tannins/acids.
    Then large water change and activated carbon again to double check. You can also do this same method using peat moss to drop the pH and then flush it with water changes and activated carbon to check to see if this method does indeed work.
    It does work.

    Non carbonate KH is more an issue for folks with higher KH's say about 3-5 degrees typically or higher.
    Obviously if you use RO or use tap with KH's of 2 or less, there's just not much carbonate or non carbonate hardness to throw you off by much to begin with.

    Say you have a KH of 10 degrees. If 3 degrees are non carbonate, you can be off by about 10 ppm of CO2 if the target is say 30 ppm.
    I measured some tanks in Ohio USA that had according to the chart, 220 ppm of CO2.
    No driftwood or anything like that. Fish were fine.

    Nuts.

    I think generally, the non carbonate issue is a problem for SOME, but perhaps not MOST.
    In most cases, the KH is by and large, carbonate. But there's enough folks with some non carbonate KH in their tap to make a muckery of all this.

    10 ppm of non carb KH is not enough to cause a huge difference. 2-3 degrees or more, certainly is, and as you get higher up, that difference only increases, so you might think at a KH of your CO2 ppm is 50 ppm, when it's actually 30ppm.
    That's a 2x difference vs the same difference at the lower ranges of CO2 ppm(say a 30 ppm target).
     
  8. dutchy

    dutchy Plant Guru Team
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    So if I have let's say a pH of 6,5 and a KH of 8, which is a theoretically 80 ppm CO2, and fish are fine, this could be 40 ppm according to the dropchecker, caused by lower pH because of driftwood and higher KH because of rocks?

    Do rocks that dissolve Ca. into the watercolumn contribute to carbonate hardness or non carbonate hardness?

    So does driftwood produce CO2 because the acids dissolve CaCO3?
     
  9. Tom Barr

    Tom Barr Founder
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    Could be a combination of the wood(doubtful if it's well aged, or if you do frequent large water changes, or use activated carbon) and the non carbonate alkalinity.
    CaCO3 or many carbonate rocks will release alkalinity depending on their structures. Some will not. But CaCO3 will for sure.


    I would not even worry about the Ca, just the CO3.
     
  10. Gerryd

    Gerryd Plant Guru Team
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    Tom,

    Thanks much for posting this. I did not understand I think that the ppm concentration was not linear and could change so much with a small ph change.

    I saw it in action as c02 increases close to the 'limit' for each tank caused fish stress, but nice to see it laid out so clearly so I can read many times over :)

    I think I 'knew' it before but this post I think made it sink in.
     
  11. Tom Barr

    Tom Barr Founder
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    Well, CO2 doe sNOT change that much at lower ppm's, it changes a lot at the higher ranges. When folks belly ache about not being able to add CO2 because it gases their fish at above 20-30ppm, it's because they are winging it and not being careful, going slow and watching.
    Perhaps their O2 is poor, perhaps there's surface scum, perhaps the CO2 equipment is hard to adjust precisely and accurately.

    Damn, there's 101 ways to screw CO2 up.
    This is more an issue for folks trying to tweak things, GO SLOWLY.

    As you increase the CO2, you also decrease the changes you make and a SMALL change in pH = a huge change in CO2.

    I see this in my 120, the 180 has a higher buffer of CO2.
    A change of 0.2 pH units will result in glass algae and hair algae in the 120.
    But that's about 20 ppm worth of CO2!!!!

    Which is a lot frankly.

    I keep trying different ways to explain this, I have done it 101 ways so far, and I'll think of more at some point also.
    People really have a simple understanding of CO2, which is unfortunate.

    Hopefully over time, I can change that view.
     
  12. UDGags

    UDGags Lifetime Charter Member
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    Curious where in Ohio?
     
  13. Tom Barr

    Tom Barr Founder
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    Near Cincinnati, it's all limestone karst aquaifer.
     
  14. UDGags

    UDGags Lifetime Charter Member
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    That was my guess. I'm right outside Dayton. Cincy is ~30-45 mins away.
     
  15. UDGags

    UDGags Lifetime Charter Member
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    Just tested my tank and it fell dead on the chart....4.5 kH, 6.2pH and 66 ppm (no livestock in tank). This means I can turn back the CO2 and just watch the pH to dial it in most likely. It will be interesting to see how much CO2 I can get in without gassing the fish/shrimp..going to start at 30 ppm, which should be around 6.55 pH.
     
    #15 UDGags, Mar 2, 2013
    Last edited by a moderator: Mar 2, 2013
  16. Tom Barr

    Tom Barr Founder
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    You have to be careful anywhere there's karst limestone in the water table. Sounds like that might be surface river water, not well water.
    3.5KH is likely surface, not well. Might be a little non carbonate hardness in there. Still, not likely more than 1-2 degrees.

    If you have a wet/dry, 66 ppm seems fine.

    If not, etc, maybe 40-45 ppm might be the limit.

    Cranking the surface current will help maintain a higher CO2 threshold also if you do not have a wet/dry.
     
  17. UDGags

    UDGags Lifetime Charter Member
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    I actually just retested and came up with 4.5 dkH. I tend to believe the 4.5 since its what my tap water is at....doesn't really water matter just gives me a reference point.

    I'm part of the Miami Valley Buried Aquifer. I'm a bit too far north. I have a few friends that are in the limestone one. I know my ex-gf was in it.

    Yes, I have a wet/dry sump and I have a vortech at the surface making waves. I think the 66 ppm will be fine but will start lower and work my way up slowly.

    Off-topic but have you measured your 180 dissolved oxygen? I know you said you ran it at 60-70 ppm CO2 and the fish were fine. I have a LaMotte test kit for dissolved oxygen and wanted to compare.
     
  18. Tom Barr

    Tom Barr Founder
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    It ran consistently at 100% with the lights off all the time.
    During the lighting period, it rose to about 125-130%.

    This was at about 84F, so the ppm is about 7.7 ppm to about almost 10 ppm, a jump of about 2 ppm

    The canister set up never got to 100% except during the light cycle and then only about 1 hour or so.
    So the claim was 1-2 ppm increase in O2 for all my tanks that were canister that got converted to Wet/drys.
     
  19. Tom Barr

    Tom Barr Founder
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    Along those same lines as CO2 changing as you go to the higher concentrations, the temperature also plays a huge difference with metabolism of fish, and the ambient O2.

    84F( or about 28.9 C) the O2 = 7.6 ppm.
    At say 70F(about 21 C) the O2 is nearly 9 ppm.

    So you have 20% higher O2 ppm and you do not need a heater.
    Plenty of O2, slower rates of growth, less energy cost.

    This can make a huge difference in the aquarium.

    Say you just want some Amano shrimp, CRS, RCS etc, and say White clouds, then this is a great way to have a planted tank.
    68-72F seems to do very well for most species.

    Algae and dosing are much easier to manage.
     
  20. UDGags

    UDGags Lifetime Charter Member
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    Thanks, that makes sense.

    Otos/amano's are my cleaning crew. Looking into getting a couple unique plecos and than probably a shoal of tetras (or something that won't bother the shrimp). Once I figure out the fish exactly I can fine tune the temperature.
     
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