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Aqua Soil and pH

Discussion in 'Advanced Strategies and Fertilization' started by Bill, Jul 28, 2006.

  1. Bill

    Bill Lifetime Charter Member
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    It has been said that AS makes your substrate acidic.

    How long after initial setup till I can start trusting my pH readings again?
    I would like to calculate CO2 by kh/Ph.

    Bill
     
  2. Wet

    Wet Lifetime Members
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    Re: Aqua Soil and pH

    The drop in KH gradually decreased over two months for me. I used Aquasoil Amazonia over pumice, peat, and mulm in one tank, and Amazoina over mulm in another tank. I found I like soft water though and now pwc with RO/DI mixed with tap to lower KH.

    I don't care about my pH anymore after feeling confident about my CO2 injection levels.

    Hope this helps.
     
  3. Bill

    Bill Lifetime Charter Member
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    Re: Aqua Soil and pH

    So would measuring your pH and leaving it out and measuring it again in 24 hrs be an accurate way to measure CO2 with AS?

    Bill
     
  4. VaughnH

    VaughnH Lifetime Charter Member
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    Re: Aqua Soil and pH

    It is never an accurate way to measure CO2, but it will be as accurate as it always is. The key is that nothing in the water changes when it degasses except the amount of CO2 dissolved in it. The problem is that we never can be sure just how far outgassed it is, and the pH change depends on how far it outgasses.
     
  5. Tom Barr

    Tom Barr Founder
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    Re: Aqua Soil and pH

    But.............

    A sample of DI water (anyone can get some drinking water DI water at a store pretty easily) + baking soda will degas and hold the SAME CO2 content at the same time as the tank's AS sample..........

    Both samples should have the same CO2 content since the partial pressure of CO2 is also the same................at least after say 1-2 days.

    So if you wanted to do this to get the CO2 ppm in a peat water, ADA AS water, you can.

    One measurement issue with the timing of the sampled CO2 can be overcome by a simple CO2 reference using pure water and the bicarbonate (KH) buffer to determine the CO2ppm and then assume this partial pressure of CO2 to be equivalent after say 48 hours or both samples under strong aeration for several minutes to degas.

    It is possible and should be as effective as the pH/KH table is.

    Regards,
    Tom Barr

    Regards,
    Tom Barr
     
  6. VaughnH

    VaughnH Lifetime Charter Member
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    Re: Aqua Soil and pH

    I agree, but it would be much more accurate than the ph/KH tables, since it would not require assumptions about sources of alkalinity or acidity. My only reservation about trying to use this method is evaporation of the samples as they sit there outgassing. Evaporation raises the KH. That kills the equation that relates pH drop to ppm of CO2. But, I don't have my head working well enough to see if the evaporation of both the reference sample and the tank sample, assuming both are in the same size and shape vessel, raising both of their KH's would compensate. Maybe when my brain is ready to shift into high gear again I will try to figure that out - but I hope someone with a finely tuned brain will beat me to it.
     
  7. Wet

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    Re: Aqua Soil and pH

    Could top off with more RO/DI if its very important to you. In the end such a skewing of the data is probably less than the %error of the test, so you can ignore it. Better guess is the most realistic goal with any hobby grade kit.

    However, if you reconsitute KH of DI with known (weighted) bicarb, dependency on the KH test is gone and then its just the (in)accuracy of the pH test you care about. (Thinking realistically.)
     
  8. VaughnH

    VaughnH Lifetime Charter Member
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    Re: Aqua Soil and pH

    In my condo 48 hours sitting on the kitchen counter in a wide mouth container would result in evaporation of about half of the water, and that would double the KH. You can add more DI/RO water to make up the difference, but that water would have to have been degassing alongside the other samples. Now, how do you make up the water loss in the tank sample? Would adding DI/RO water from an outgassed supply do it? Yes, tentatively, it looks like it would.

    I threw up my hands when contemplating how long such a test would take, and all of the new errors that might be introduced. My last try was blowing into a sample of RO water to see if a repeatable amount of CO2 could be introduced without causing me to faint first. That's when I gave up totally on measuring CO2.
     
  9. Tom Barr

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    Re: Aqua Soil and pH

    Evaporational increases in KH can easily be dealt with by using a larger sample that's less influence in terms of the toal volume lost due to evaporation and salt/TDS increases.

    If you use a shallow tray with 5mls, in 24hrs, it will be all gone:)
    If you use 500mls and place in a glass, it will not obviously.

    We can assume that the evaporation rate will be the same and much more so when you are dealing with 500mls vs 5mls.

    Still, it's better than the KH/pH table.

    Regards,
    Tom Barr
     
  10. Tom Barr

    Tom Barr Founder
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    Re: Aqua Soil and pH

    This would work using the RO/DI make up water if the water(RO/DI) was also exposured to the air and equal with the partial pressure.

    Size of the smaple sat out also will make a difference.
    You only need to do this a few times, maybe 1-2x to get that pH drop needed and then thereafter if the plants are not responding right or the fish seemed CO2 stressed etc.

    Once you are in the ball park, a little visual tweaking will do the rest.

    Still, this is a better method than the pH/KH table since it works on most any type of tap/peat/ADA AS etc.


    Regards,
    Tom Barr
     
  11. VaughnH

    VaughnH Lifetime Charter Member
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    Re: Aqua Soil and pH

    I agree. This method looks promising, and once you find that, in your kitchen, using your brandy sniffer, after 48 hours a water sample has, say, 0.7 ppm of CO2 in it, all you need to do after that is just let the tank sample sit for 48 hours in the same size brandy sniffer, measure its pH and compare it to the in-tank water. Then use the equation CO2 ppm=(Degassed CO2 ppm)X10exp(degassed pH - in tank pH) to calculate the CO2 ppm in the tank.
     
  12. Tom Barr

    Tom Barr Founder
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    Re: Aqua Soil and pH

    Yep, by using that good old partial pressure = for any sample and using the difference in pH due solely from the addition CO2, these are good safe assumptions, we can radically change the way folks measure CO2 ppm and provide a method to measure CO2 that gets around alkalinity/tannins issues.

    I don't think anyone has suggested it like this before really, I've been kicking this around in the back room for a little while.

    I've given this a fair amount of thought as to why this would NOT work, what are the possible measuring issues etc. I'm still coming up empty there.

    So about time to let it out.

    Humm.......I suppose I need to write the method up in a simple clear way(Muhahaha!!) :gw
    Now, can I take my own advice or not? :gw



    Regards,
    Tom Barr
     
  13. VaughnH

    VaughnH Lifetime Charter Member
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    Re: Aqua Soil and pH

    I stuck the method in the planted tank forum to try to get several people to try it and report what they found. I may try it myself today if I feel up to it. But, my pH meter may have dried out by now from lack of use. I seriously doubt that I will ever do this method twice - I like my own "watch the fish and algae" method much better. (Even if it does treat the fish a bit badly.)
     
  14. Tom Barr

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    Re: Aqua Soil and pH

    Well, it's mainly just an alternative method that avoids some of the issues folks have raised with using the pH/KH method alone.

    That's the main use, otherwise the pH./Kh chart to get close and then a little tweaking is all that's needed.

    Some whine about not being able to measure their CO2 ppm when usuing the ADA Aqua soil. So that's a response to that as well.
    I gave a similar method for the folks that complained about not being able to measure the CO2 when they used tannins/peat etc also several years ago.

    But beyond that, the KH funnyiness many experience can also enable folks to get around those issues also.


    Regards,
    Tom Barr
     
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