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pH or kH change to increase CO2

Discussion in 'Advanced Strategies and Fertilization' started by mstolpner, Dec 17, 2005.

  1. mstolpner

    mstolpner Junior Poster

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    Hi,

    I started 135G about a month ago. Everything seems fine except that I have different algae - not much but noticable. I think it's BBA, green spot and thread algae. My current kH is 4 and I keep pH with controller at 6.4 (on with lights only). Using ph/kh scale I calculate 48ppm CO2 but all the fish is doing great. From what I can find it's recommended to increase CO2 level to fight algae. So what is better: increase KH or decrease pH?

    Other parameters: PO4 at about 2ppm, NO3 at about 10-20 ppm, temp 26C, open top, light - 3x150W MH for 4 hours midday and the rest 6 hrs - 2x96W PC. I think it's heavy planted but not quite sure - there are over 30 plants of different size. I didn't add PO4 yet as it was too high initially (>5ppm). I think it came from the eco-complete as there is none in our water.

    Thanks,
    Mikhail
     
  2. Spar

    Spar Guru Class Expert

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    Re: pH or kH change to increase CO2

    changing your KH or pH values will not affect co2. co2 can only be altered by adding co2 or laying off co2. i.e. co2 is independent of either value, while pH is dependent on co2.

    also, throw away your po4 testkit and start doing 1/16t per 20g's anyway. those testkits lie and have caused problems in my tank before. unless you have severe plant decay or over-feed fish flakes bad, you wont have po4 problems.
     
  3. Tom Barr

    Tom Barr Founder
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    Re: pH or kH change to increase CO2

    I'm not certain the nutrients are the right amounts from your test kits.
    PO4 in particular.

    Add some KH2PO4 and see if that helps.
    If you are at 2-5ppm, adding another .5-1.0ppm is not going to cause any issues.

    Are you adding KNO3 etc?
    Light and CO2 seem fine, if you want more CO2, you just add more.
    Changing the pH will occur as you do that by driving the pH down with CO2.
    KH is fine.

    GH?

    Regards,
    Tom Barr
     
  4. mstolpner

    mstolpner Junior Poster

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    Re: pH or kH change to increase CO2

    I am using controller that keeps pH to predefined level of 6.4 by adding CO2. I can change the CO2 amount by changing predefined pH level or by increasing KH which is 4d now. So my question is should I add more CO2 and keep KH the same or should I also add baking soda to increase KH?

    I don't really rely on test kit. Most of plants (aponogeton, echinodorus, crypts, lotus, banana plant, ...) are doing great and pearling. Aponogeton and Echinodorus are blooming like crazy, so I assume that PO4 level is really significant. Would it heart if I still add PO4? How much?

    Thanks,
    Mikhail
     
  5. Spar

    Spar Guru Class Expert

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    Re: pH or kH change to increase CO2

    I wouldn't mess with KH. just change the pH value on the controller. just watch your fish's actions after changing it to make sure not too much is being added. I had fish jumping this morning until I realized my co2 was dumping out of my unit... estimated about 120ppm co2 :eek: easy fix though luckily with no deaths.

    as for how much kh2po4 to add, it is up to you. if the thoery of excess nutrients not causing problems holds true (which seems to be the case), then adding what EI recommends (1/32 - 1/16 tsp per 20g's, 3x per week) on top of what is already claimed to be in your water, will NOT hurt anything. That includes plants, fish, and algae.

    Therefore, begin adding that much.
     
  6. mstolpner

    mstolpner Junior Poster

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    Re: pH or kH change to increase CO2

    Thank you, Spar. I will give it a try. Mikhail
     
  7. mstolpner

    mstolpner Junior Poster

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    Re: pH or kH change to increase CO2

    Tom,

    Sorry, I missed your response. I am changing 10% (~10G) water every day and I am adding 10ppm (in 10G) KNO3 and 1d GH using Seachem Eq. Test kit measures 4d GH. Should I add more Seachem Eq?

    I used CSM+B but today I decided to try TMG. I've never seen so much pearling in my aquarium yet. I think I will keep using TMG. I found it 5L for 99CAD at Big Als. I think it's about 1 year supply so this is not too bad.

    Thanks,
    Mikhail
     
  8. aquabillpers

    aquabillpers Lifetime Charter Member
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    Re: pH or kH change to increase CO2

    That is true in a tank in which CO2 is injected. However, in a non-injected tank, CO2 in almost nonexistent when the pH is above 8.4. There, CO2 is dependent on the pH, not the other way. The plants that live in high pH environments get their carbon in other ways.

    Bill
     
  9. Spar

    Spar Guru Class Expert

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    Re: pH or kH change to increase CO2

    i don't think that is quite right. co2 is part of the formula that creates pH. same with KH. that high of pH values are that high due to certain salts (lake rift-lake salts) and general carbonates.

    also, the atmospheric levels of co2 are at 3ppm, so as long as the tank isn't in a vaccum :rolleyes: there should always be some co2 present. at least for our hobby purposes.
     
  10. aquabillpers

    aquabillpers Lifetime Charter Member
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    Re: pH or kH change to increase CO2

    Sure, injecting CO2 will reduce pH at "normal" levels, but there is a point beyond that at which the mineral composition of the water won't allow it.

    In a high pH environment the amount of disolved CO2 is minimal. Test that. Determine the CO2 at normal levels, increase the pH to 9.0, and retest. There won't be any. Inject a lot of CO2. There still won't be any. I'll leave it to the chemists to explain why.

    People with water with very high pH (8.4 and up) are pretty much restricted to plants that can obtain carbon from other sources than dissolved CO2.

    Bill
     
  11. Spar

    Spar Guru Class Expert

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    Re: pH or kH change to increase CO2

    the incremental decrease to pH from injecting co2 is extremely small at high KH values. i.e. if you have something around 20 dKH, injecting 10ppm co2 will barely budge pH. That doesn't mean that it isn't present. And your measurements may be skewed anyway since even a slight off-pH reading of say .05 pH will make a difference in the co2 calculation.

    Also, unless you specifically add the special minerals (rift-lake salts being one of them), and assuming you don't add something like Peroxides to your tank to alter pH other ways, the highest possible pH you can bring your tank to is 8.2. Even if you dump 10 pounds of baking soda in your water, pH will not go above 8.2.

    Thus my new argument would be that people that have higher than 8.2 pH (in that 8.4-9.0 range you mentioned) are adding something else to their water that merely makes the testing of co2 non-effective.
     
  12. aquabillpers

    aquabillpers Lifetime Charter Member
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    Re: pH or kH change to increase CO2

    Hi,

    Sorry. Water that flows over limestone regularly tests at 8.4 to 9.0 or higher
    Lake Tanganyika maintains a pH of 8.4 to 9.0 without benefit of salt additions, just by using what is there naturally. I dont believe that the lake has a lot of plant life, either, maybe because of lack of carbon, at least in part.

    I believe that if you had a tank with a pH of 8.2 (and sufficient kH to support that level), you could inject CO2 until the cows came home without significantly changing pH and without increasing the dissolved C02. But others are more knowledgeable than I on that. See the table at: http://www.thekrib.com/Plants/CO2/kh-ph-co2-chart.html

    You might do some research into pH and water. Here's a place to start:

    http://www.austinpondsociety.org/wwwboard/messages/852.html

    Bill
     
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