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Co2 for water softening?

Discussion in 'Water Chemistry' started by Neil Groves, Feb 1, 2016.

  1. Neil Groves

    Neil Groves Member

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    I have tried the peat granules for lowering my pH and nothing...nada...zilch

    I have been contemplating Co2 for my plants so was reading about it and it mentions something about it being able to lower the pH too?

    is Co2 easy to use or will it open up a whole new can of worms for me to deal with?

    Neil.
  2. gerald

    gerald Well-Known Member 5 Year Member

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    adding CO2 will lower pH, but i dont think it has much direct effect on Ca or Mg ions (GH hardness). It will however cause plants to grow faster, and the plants will consume some of the hardness ions.
  3. Neil Groves

    Neil Groves Member

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    Thankyou.....sounds like a job for the weekend.

    Neil.
  4. dw1305

    dw1305 Well-Known Member 5 Year Member

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    Hi all,
    I'm not a CO2 user as I can find enough ways of killing the fish without adding another avoidable one, but Gerald is right when you add CO2 you don't soften the water, you just change the HCO3- ~ CO2 equilibrium point, it doesn't change the water chemistry just the ratio of H+:OH- ions.

    Calcium carbonate (CaCO3) is insoluble in pure H2O, but H2O in contact with the atmosphere has a very small amount of CO2 diffuse into solution (it is about 0.5 ppm). This low level is because, although CO2 is very soluble in water, it only forms 0.04% of the atmosphere. Carbonates are however soluble in acid, and the acid in this system is carbonic acid (H2CO3), which forms from a very small percentage of the dissolved CO2

    If you have a buffer of carbonate (so some dKH) the carbonate mineral will go into solution as 2HCO3- and usually Ca++ ions (calcium carbonate is less soluble than sodium carbonate (Na2CO3) etc.), at 400ppm CO2 this equilibrium is stable at ~pH8.

    When we add CO2 we add more H2CO3, which disassociates into H+ and HCO3-. We've added extra H+ ions, so the pH, the ratio of H+:OH ions falls. When we stop adding CO2 things return to normal.

    How far it falls depends upon how much acid (CO2) we add, and the dKH of the water. If we add about 30ppm CO2, (enough to asphyxiate more oxygen demanding fish) we will have a pH drop of about 1 unit from the pH at atmospheric levels of CO2, whatever our starting dKH was.

    Drop checkers use a narrow range pH indicator (bromothymol blue) and a 4dKH solution to allow you to estimate the CO2 from the pH drop.

    The "one unit = 30ppm CO2" works because pH is a log10 scale, and if you plot an exponential curve on a log10 scale you get a linear trend. Details are here: <"UKAPS: Question about ..">.

    cheers Darrel
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  5. Neil Groves

    Neil Groves Member

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    Not being a scientist, I understood very little of what was just said...

    So what is the bottom line here?....is it a good idea to use co2 ?
  6. gerald

    gerald Well-Known Member 5 Year Member

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    Welcome to the finnicky world of soft-water fish keeping. Soft water species like Apistos, Dicrossus, and certain Bettas and Gouramis can be tricky because their water conditions are just not as stable as in hard-water tanks. You may end up learning a bit more chemistry than you'd planned on, but it'll be well worth it, and you'll have a good reason to apply it.

    I think most of us here don't use added CO2 with Apistogramma, which are often more sensitive than the tetras, rasboras, barbs, rainbows, etc often used in high-tech planted tanks with CO2. Since Apistos can be expensive and/or hard to get (except for a few common species) and since many of us want to breed them, we'd rather not subject them to the added stresses of CO2 (and fertilizer additives used in high-tech). Used carefully it can work, but like Darrel says, there's enough other risks in fish keeping already.

    If you're using a public water supply, the water provider usually has "finished water" chemistry data available on a website, or by a phone call. Ask for the hardness (what aquarists call GH) and alkalinity (what aquarists call KH), if you dont have a test kit to measure it. If hardness is greater than about 70 mg/L (about 4 degrees GH) then you'll probably need either RO, ion exchnge, or rainwater to soften it, if you really need soft water. Alternatively, you can choose to keep species that can tolerate higher pH and hardness, like tank-bred Apisto cacatuoides, macmasteri, borellii, alacrina, ...

    My tap water In Raleigh NC (and many other places) is fairly soft (1.5 to 2 dGH and dKH) but the pH is high initially (about 8.2). Our water treatment plant adds sodium hydroxide to keep the pH high and prevent water pipes from corroding (remember Flint, Michigan?), but it doesn't add much KH, so the pH drops pretty quickly in an aquarium where acid is produced by the bacteria consuming the fishes' waste.
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  7. Neil Groves

    Neil Groves Member

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    I think your right, I'm going with killifish since they are hardwater fish and higher pH, I can play with them while I set up another tank and experiment with water parameters. not only that but since I am wanting to breed these guys, I am best waiting till I can set up a tank just for them anyway.

    thanks for all your help guys.

    Neil.
  8. dw1305

    dw1305 Well-Known Member 5 Year Member

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    Hi all,
    Added CO2 increases plant growth, when all the other plant nutrients are available.

    Would I use it? I wouldn't.

    Is rain-water an option?

    cheers Darrel
  9. Neil Groves

    Neil Groves Member

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    I get 3 months rain per year here in California ( jan-march) so no, I don't have the luxury of rain water...

    Neil.
  10. MickeM

    MickeM Active Member 5 Year Member

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  11. Neil Groves

    Neil Groves Member

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    Lmao.....nice idea but I think my neighbours may have a problem with this...

    I'd probably need planning permission too
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  12. gerald

    gerald Well-Known Member 5 Year Member

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    Last year i visited the Torrey Pines Preserve north of San Diego CA, where the Torrey Pines catch and condense fog with their leaves the same way those fog nets in the Atacama Desert do. There's not enough rain there to support most trees, but lots of morning fog. Each leaf (pine needle) has a groove to channel the condensed water to the base where it drips onto the soil beneath the tree. (Sorry to derail your post Neil)!

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  13. dw1305

    dw1305 Well-Known Member 5 Year Member

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    Hi all,
    I was going to say we are lucky, because it has rained here pretty much every day since September, but maybe lucky isn't quite the right word.

    If I had 10,000 litres of rain-water storage, rather than about 1000, I could have filled it up 10 times over.

    cheers Darrel
  14. aarhud

    aarhud Active Member 5 Year Member

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    Neil,
    Your other option is an RO unit. I'm not sure about your water rates in CA, but these units do tend to use a fair amount of water because the ratio of "waste" to to "clean" water is going to be somewhere in the neighborhood of 1:3-1:5. You also have the cost of the unit itself.
  15. Neil Groves

    Neil Groves Member

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    I have an R/O unit sitting in my garage brand new still boxed, been there for 3 years, I won't use it because I'm on a water meter here and the waste is way too much for me to want to pay for.
  16. aarhud

    aarhud Active Member 5 Year Member

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    Completely understand, I have been on a meter the past two years and HATE it. You are finding out why a lot of fish keepers do not fight their water. I think Gerald pretty much summed it up. You can still enjoy more forgiving species.
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  17. Karin

    Karin Active Member

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    Give a try to Borelliis... they are pretty nice. And very prolific!