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KH and CO2 relationship

Discussion in 'Advanced Strategies and Fertilization' started by gpdiver, Jul 18, 2005.

  1. gpdiver

    gpdiver Junior Poster

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    I have measured my tank with a Tetra Kh test and get a 4.0. I recently measured with a Lamotte Alkalinity test and it measured a 140ppm which is almost double the tetra test.

    I have CO2 injection with a ph controller and have calibrated the ph meter. The ph is about 6.6 which I thought was yielding 30ppm according to the tetra Kh number. The fish are OK which I would believe they would be struggling if the Co2 was actually 60 ppm (if the Lamotte is correct).

    My Kh from the faucet is also 4.0. I have3-4" of 100% eco complete as the gravel. I live in the Houston area and the water is fairly hard.

    Any idea which test correlates with the ph-KH C02 charts? I saw an old post from George Booth last evening that suggested maybe the tetra test was better. I'm happy with my CO2 system (external reactor) I just want some reassurance as to what the CO2 may be.

    I appreciate any feedback.
     
  2. Spar

    Spar Guru Class Expert

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    Re: KH and CO2 relationship

    you said your tap water is 4.0 KH? Do you know this for sure? if so, test both the testkits against the tap water and whichever one shows ~4.0 is better.

    do the bottle have expiration dates on them? sometime the number look screwy, but it is usually obvious at least which year it was manufactured. the newer one is generally more "trustworthy".

    they should all return the same value, so one of them is obviously malfunctioning.

    as an alternative test. get a 5g bucket of tap water. test the KH with both testkits, record the result. add 1/2t of baking soda to the bucket, stir well. wait about 5-10 minutes. retest with both testkits. whichever one shows an increase of 5 dKH (90ppm) is the most effective kit.
     
  3. gpdiver

    gpdiver Junior Poster

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    Re: KH and CO2 relationship

    Good suggestion, but I expect that both test kits will show a move. I tested the water from my faucet with the tetra test kit, so I do not know for sure what the water Kh is. Both test kits are new.

    I suspect the Lamotte test is high, but I am not sure if the Lamotte test under my circumstances (hard water in Houston, ph 8, Gh 11) are affecting the Lamotte test. Also, not sure if the tables developed(for calc. Co2) were developed with more basic kits, like tetra.
     
  4. Spar

    Spar Guru Class Expert

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    Re: KH and CO2 relationship

    sounds like you are pre-assuming that the tetra testkit is the one that is fine though. in my experience, tetra has always been the least reliable of the manufacturers. Lamotte makes some high quality products.

    the pH/KH/co2 chart is not based on a certain testkit. all testkits, assuming functional, will read the exact same KH (within reason), regardless of the manufacturer. same goes with whatever pH testkit you use; although a digital is going to get you a more exact reading.

    do the testkits give you consistent readings? meaning, if you were to test your tap water 5 times with the same testkit, does it jump around (even by 1 dKH at a time)?

    also, 11 dGH isn't necessarily hard. and you can not pre-judge a hard alkalinity (high KH) based on pH or KH out of the tap. Dallas has an extremely soft water (2 KH & 7 GH), but the tap water comes out at near 8.5-9.0. After setting the water out in a bucket overnight with an airstone running, you see the pH drop down to 7.2. the higher pH at first is due to gases in teh water supply... giving us a false reading.

    That may be a good idea for you actually to know for sure. based on the atmospheric level of co2 being ~3, it is expected for a KH level of 2 (in dallas) to drop the pH to 7.3 (close to what I measure overnight). If you did the same thing you could run a test at whatever pH you get in the morning (use a digital if possible), and keep changing the KH on the table until you see what gives you a co2 level of ~3. this is not full-proof but it will definately distinguish between a KH of 4 and 8. big difference on the table and outcome of pH. always fun to do an experiment anyway :)
     
  5. gpdiver

    gpdiver Junior Poster

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    Re: KH and CO2 relationship

    Both tests are repeatable. I checked both 3 times over 3 days as I was a little set aback by the difference. The only reason to suspect the tetra is more in line with the charts is that I find it difficult to believe the CO2 is 60 ppm with no signs of fish distress and a calibrated ph meter (also checked with a handheld ph meter). I agree with the quality of Lamotte and have really like the No3 and Po4 tests.

    Any other insights also appreciated. Thanks
     
  6. Tom Barr

    Tom Barr Founder
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    Re: KH and CO2 relationship

    Call the water dept, ask what they send to the consumers specifically in your area.

    Alkalinity is very closely monitored.
    Compare their's with your Lamotte kit.

    You can also do 0.5 degree units with the Tetra by using 10mls instead of 5mls. Each drop counts 0.5 degrees instead of 1.

    Etc.........

    Regards,
    Tom Barr
     
  7. gpdiver

    gpdiver Junior Poster

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    Re: KH and CO2 relationship

    No luck from the water dept yet, but I believe I have the answer. I borrowed a lamotte CO2 test and the CO2 was about 60ppm. So, I guess the lamotte alkalinity test is correct.

    I also have the lamotte Calcium hardness test 3609. Does this also relate to KH. This is not the test that measures calcium and mg hardness.
     
  8. imatrout

    imatrout Prolific Poster

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    Re: KH and CO2 relationship

    I hate to suggest yet another test kit, but I was having the same issue between a Salifert and AP KH test. I got a Salifert CO2 test kit and though it is not really easy to read (tritation colors change slowly rater than distinctly), I was able to get a pretty good read on CO2 levels between the 3 kits.
     
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