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The Red Sea CO2 Indicator

Discussion in 'CO2 Enrichment' started by shane, Dec 8, 2006.

  1. shane

    shane Lifetime Charter Member
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    I recall reading something on this forum from Vaughn that mentioned using a known KH sample and pH liquid to find out how much CO2 is in the tank. I have a Red Sea CO2 indicator in my tank. The only problem is I have no idea what green means in terms of how many ppm CO2 is in the tank? Anybody have any idea what green means translates ti in terms of ppm for the Red Sea CO2 indicator?
     
  2. VaughnH

    VaughnH Lifetime Charter Member
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    DIY Drop Checker - Aquatic Plant Central- aquascaping...a living art should answer the question. You need to make your own KH standard water, using distilled or DI water so you are sure there is nothing else in that water that affects the acidity or alkalinity except for the CO2. The Red Sea indicator water will have the same ppm of CO2 in it as the tank water has, and you can measure the ppm in the indicator because you know that water is "perfect" for doing so.
     
  3. shane

    shane Lifetime Charter Member
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    The liquid that comes with the red sea kit? Any idea what it is? Is it pH liquid?
     
  4. VaughnH

    VaughnH Lifetime Charter Member
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    I'm pretty certain it is just pH reagent, the same as is used in pH test kits. The amount you add to the bulb is not critical so just add enough to get an easy to see color.
     
  5. Mr G

    Mr G Junior Poster

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    I've just tried the method with the 4dKH reference solution and it looks to be working really well ...
    [​IMG]

    What I've also decided to try were a couple of other CO2 test methods to compare results.

    I had an old Red Sea CO2 test kit and tested the water with this....
    I also checked my PH and KH and put this through the usual charts ....
    A neighbour have me an old JBL permanent test kit, this is now also in the tank (tank water + reagent) ...

    The results:

    Drop checker with KH4 solution/bright green colour = 30ppm
    Red Sea Co2 kit (liquid reagent type) = 64ppm !!!
    PH/KH PH=7.0 Kh=13 CO2=39ppm
    JBL permanent test kit = Co2 between 24 - 36ppm

    =====EDIT=====
    The fish and shrimp in my tank are all doing fine, no signs of stress from high CO2 levels ...... So i'm fairly sure the Red Sea kit's reading of 64ppm is way off the mark !!!
    =============

    The only one of the above methods that does NOT rely on tank water is the one that VaughnH and Tom have discussed on here. :cool:

    I dont add any PH/KH adjusting/buffering agents, the substrate is ADA Aquasoil (known to impact on PH & KH) and the ferts are ADA ferts (brighty K & Step2), but this tank will be running EI as from next week.

    Interestingly the JBL kit says it can measure Co2 only if "there are no other substances in the water which lower PH (e.g peat, PH-lowering agents, Nitrate).
    Does NitrAte influence the reading of PH/KH/Co2 tests ?

    I'm also checking the water using the method of looking for a drop of 1 PH in degassed water. I'll look at this tomorrow, my normal tap PH is about 7.8.

    Cheers
    Al


    P.S. I've mentioned this reference KH solution method over on the planted tank section of Tropica Fish Fourms, Hope thats OK, I gave due credit for all the hard work done by VaughnH & Tom on this method. Just wanted to spread the word a bit !
     
  6. shane

    shane Lifetime Charter Member
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    Interesting results.

    How do you create the perfect KH=4.0 solution? Use distilled water and then what?
     
  7. Laith

    Laith Lifetime Charter Member
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    Baking powder (sodium bicarbonate).
     
  8. Tom Barr

    Tom Barr Founder
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    The KH reference notion is Vaughn's idea and it's application to the visual drop checker, not mine.

    I'd thought of a pH version with an air gap, but quickly realized some problems with that and switched to a membrane pH probe seperator.

    Vaughn, you need to consider a larger thin version of the drop checker without any air gap, just the reference solution seperated via the membrane.

    That would greatly enhance the response time.
    More surface area and thin(but enough depth for decent color resolution), just a snap box that you could fill the KH ref solution into and seal with the membrane to the tank water.

    Sort of like those SeaChem NH4 thingys folks use.
    Humm.......I suppose I could call Greg Morin and tell him.

    Seems like a good idea.

    Al, I think they believe most NO3 issues are from fish, thus the production of HNO3, nitric acid which can mess with things.

    Regards,
    Tom Barr
     
  9. shane

    shane Lifetime Charter Member
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    How does one really dial the solution to KH=4 though? Get a large sample of DI water, approximate the sodium bicarbonate needed to dial in the solution to KH=4, and then use a KH test kit to see how close you are?
     
  10. VaughnH

    VaughnH Lifetime Charter Member
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    The way I used to zero in on a 4 or 5dKH distilled water solution was to start with about a cup of distilled water. Add a very tiny amount of baking soda. Then test a sample with a 4X size sample - I use a narrow bowl wine glass to make it easier to see the color. With the AP test kit, one drop normally equals one dKH, but with 4X sample size one drop equals .25 dKH. If you have supreme good luck your water is found to be at the KH you want. If not, it will almost certainly be too high. Guess at how much more distilled water is needed to dilute it down to the KH you want and add that. Do another test. When you repeat this a few times you get the KH you want, and if you really want better accuracy then, use 10X sample size for the last KH test. I had great luck making 4 dKH water, but lousy luck making 5 dKH water. I ended up with 6 dKH, and mixed half and half with 4 dKH to finally get it at 5 dKH.
     
  11. Mr G

    Mr G Junior Poster

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    VahughH,
    Just wanted to say that I love this method of yours - Great work !

    As for mixing the solution: I started with 100ml of distilled water and a Nutrafin KH test kit. When adding the bicarb of soda I used the tiny measuring spoon that comes with a Tetra NO3 test kit, I don't know how much it holds, but it's tiny !

    Initially I used the normal amount of water for the Nutrafin testkig (5ml) and added tiny amounts of bicarb, once was getting a reading of 4dKH, I increased to 10ml and repeated. As this was my first attempt at this method I stopped there.

    Next time I'll go 4x the amount of water to achieve greater accuracy.

    Al
     
  12. VaughnH

    VaughnH Lifetime Charter Member
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    Thank you Al! I wish I could take all of the credit for the method, but Dennerle was using it before I ever heard of it, and I really got the idea from "Gomer" (Tony Gomez), who casually mentioned using distilled water in the bulb instead of tank water, which led me to try to prove he was wrong about that. Like many of my "proofs" I ended up proving that he was right, and then just reasoned out why he was right. I hope the idea gets spread widely enough that all of the "aquatic plant gardeners" know about it. That's why I have become a nag in always recommending it on all of the forums I visit.
     
  13. Mr G

    Mr G Junior Poster

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    Well then I owe some thanks to Dennerle and Gomer ... but thanks for highlighting it :D

    Well I've posted my attempt at this method on Tropical Fish Fourm's ( HERE ) just trying to spread the word a bit.

    I'll certainly be using this method for now as it seems far more accurate than others.

    Al
     
  14. VaughnH

    VaughnH Lifetime Charter Member
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    Al, I notice some are asking "how do you know that the ppm of CO2 in the bulb is the same as in the water?" The answer is: If there is a sealed quantity of air in contact with water which has CO2 in it, remembering that CO2 goes into and out of solution with water very easily, the air will soon reach an equilibrium with the water, with as much CO2 entering the air as is leaving it. Now, if that air is in contact with a sealed bit of water, that water and the air will also reach an equilibrium, with as much CO2 entering the water as is leaving it. No matter what the actual amount of CO2 in the air gap is, the equilibrium will be such that both batches of water will reach the same concentration of CO2. I tested this and reported the test on APC, at:DIY Drop Checker - Page 5 - Aquatic Plant Central- aquascaping...a living art. You might want to add this explanation to your discussion.
    Edit: You can do a mind experiment to prove this too: Assume a large body of water "A", with CO2 concentration C1, connected to an air passage "B", with CO2 concentration C2 in equilibrium with C1, connected to another small body of water "D", with CO2 concentration C3. Now assume that C3 is less than C1, therefore not in equilibrium with C2. That means more CO2 molecules will move from B to D than from D to B, which raises C3 until C3 is in equilibrium with C2. But, at equilibrium, the concentration in air is C2, so the concentration that is at equilibrium with C2 must be C1, since we already said that concentration was in equilibrium with C2. So, C1 and C3 must be the same. You can use the same logic for the case where you assume C3 is greater than C1.
     
  15. Mr G

    Mr G Junior Poster

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    Many thanks VaughnH, I've posted that explaination.
    Hopefully it will help to spread the word a bit further.

    Actually now I've given this method a try and just re-read the APC thread it all makes much more sense than when I read it before actually giving it a go !

    Cheers
     
  16. detlef

    detlef Subscriber

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    Shane,

    here is what has worked for me in creating my own ref KH solution:

    0,6g of NaHCO3 into 100ml of distilled water make 200°dKH. If you enter 10ml of this solution into 490ml of distilled water you'll end up with about 4°dKH.

    If you don't have a balance pharmacies will likely help you out weighing small amounts of NaHCO3.



    Best regards,
    Detlef
     
  17. shane

    shane Lifetime Charter Member
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    Thanks Detlev,

    How accurate are the KH test kits like AP, etc? Can one use these test kits and get the results needed?
     
  18. detlef

    detlef Subscriber

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    Well,

    KH test kits don't seem to be very accurate which is not surprising though. See Tom's thread on "KH reference dosing". My cheapo Tetra test kit measured a little more than the calculated 4°dKH. It gave me around 5°dKH.


    Regards,
    Detlef
     
  19. shane

    shane Lifetime Charter Member
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    Ya, I have a test kit that uses titration to measure KH.
     
  20. VaughnH

    VaughnH Lifetime Charter Member
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    The Aquarium Pharmaceuticals KH test gives one dKH per drop of reagent in the test tube sample. If you use a double size water sample, each drop gives .5 dKH. And, if you use a 10X size water sample, each drop gives .1 dKH. The drops are not always exactly the same size, so the error in the test is probably around +/-10%, if not more. But, that isn't very important for measuring ppm of CO2, because the CO2 ppm is directly proportional to the KH, where it is proportional to ten raised to the power of 7 minus the pH. This makes pH errors much more significant. Fortunately the pH test is not at all sensitive to how many drops of reagent is used per test, so you can use the amount that makes the color most obvious to you.
     
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