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Ideal pH question

Discussion in 'Water Chemistry' started by Jerry Pritchett, Jan 26, 2017.

  1. Jerry Pritchett

    Jerry Pritchett New Member

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    When researching a subject I have always found it useful to read as much source material as practical and evaluate the information based on those with the most practical and scientific based knowledge.
    I have had some differences I have found in what is the ideal pH to run an aged system at.
    Murray and many others put 6.8-7.0 as the sweet spot
    Nate Story and others state that 6.0-6.4 is the sweet spot.
    My tentative conclusion I have drawn from these differing opinions is that the lower range is the sweet spot if you are most interested in plant production and not fish growth. This would mean that the higher range leans toward fish growth as just as important as plant growth.
    Both Nate and Murray have enough experience in aquaponics that it is not easy to dismiss either ones opinion. I will say that Nate apparently came to aquaponics through hydroponics which uses much lower pH levels than aquaponics which may influence his thinking.
    I have no doubt that either range will work. I would like to hear any other thoughts on this and if anyone thinks I am on the right track with this or not.
    Bear in mind that I am referring to a system that has aged to the point of stability, not a new system.
     
  2. Yabbies4me

    Yabbies4me Administrator Staff Member

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    The pH in most systems start in the mid-high 7's, or even low-mid 8's, depending on your source water of course. After a while the pH in a system will begin to drop naturally due to acids produced by the nitrification process consuming the carbonates in the water.

    If you catch that pH decline in the high 6's then the water most likely still contains a reasonable amount of carbonates, making it easier to manage and maintain pH, especially if you use some carbonate based products for controlling the pH and/or high carbonate top-up water.

    If you allow the water pH to drop down around 6.0 before intervening, then there is little or no carbonates left in the water, making it much harder to control and maintain the pH. It requires more frequent testing and the addition of much more pH raising agent/s, much more frequently, especially if you subscribe to Nate Storey's recommendation of not using any products containing carbonates, only hydroxides.

    A pH up in the high 6's (I recommend 6.8 to my customers) strikes a happy medium between plant and fish requirements, and makes it a little easier to control and maintain the pH, especially if you top-up with water containing carbonates. In that situation many people have found they don't need to add much, or even any pH raising/buffering products, especially in summer when they are adding much more top-up water.
    .
     
  3. Jerry Pritchett

    Jerry Pritchett New Member

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    Thanks for your reply and information. I did forget to add that my water source is rain water. We have a lot and will not have to use water with carbonates in it rarely if at all. The water rural water we have is low in carbonates even if we have to use it occasionally.
    If I am tracking with you on this I should be using calcium & potassium carbonate instead of the hydroxide form since I am using rain water as my primary source of water. Is that correct?
    It didn't occur to me that the use of whether to use the carbonate vs hydroxide forms of raising pH might be dependent on the water source. I know that water sources can be vary between extremely carbonate or extremely acid and that treatment might change depending on the source used.
     
    Last edited: Jan 29, 2017
  4. Robert123

    Robert123 Active Member

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    Another benefit of the "high 6's" that Yabbies recommends..... if you run an extremely high fish loading as I do right now, you can get away with some amount of ammonia in your system without it causing damage to the fish as it is protonated making it NH4+ (less toxic than NH3). (Of course it depends on the fish. Tilapia are tough subjects :))
     
  5. Robert123

    Robert123 Active Member

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    Of the two carbonates you mention, potassium would be my choice but unfortunately it can be pricey. With that said, some here find success with natural forms of calcium carbonate.
     
  6. Danscraft

    Danscraft VIP Supporter

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    Basically between 6 to 7 is good in my experience. To my shock my largest system has got as low as pH 5 on occasions if I don't monitor it frequently enough. There were no negatives to be seen really although the plants get nutrient lockout and don't grow as well. I rectified of course but the fish didn't show any negative signs at all but I must be more careful to keep it above pH6.
     
  7. Jerry Pritchett

    Jerry Pritchett New Member

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    In reading further in this section of the forum I find that the recommendation for the carbonates is 3 calcium carbonate to 1 potassium carbonate. This is certainly more economical since 50 lbs of hydrated lime here is $9.18 and the best I can do on potassium carbonate for 10 lbs is $41.90 which is $4.19 per lb or 24 lbs at $73.77 which is $3.07 per lb. To start I will be purchasing 2.5 lbs of potassium carbonate at $6.00 per lb. Using carbonates will make since for me since I am using rainwater with practically no carbonates.
    I suspect if I was using water from the farm I was raised in western Oklahoma which had over 600 ppm of calcium carbonate I might be better off using the hydroxide forms.
     
    Last edited: Jan 29, 2017

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