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Ph low and buffering

Discussion in 'Fertiliser - mineral supplements. Aquaponics syste' started by jassouth, Oct 31, 2015.

  1. jassouth

    jassouth New Member

    Joined:
    Nov 29, 2011
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    Country:
    Australia
    State:
    NSW
    City:
    Urunga
    Hi all
    Have a 2 year system that is going great haven't tested the water for a long time and recently tested the water to find that my ph was at 6 or lower.
    So treated my KH and it was sitting at 0.
    so got some potassium bicarbonate and started adding a scoop morning and night after testing.
    In total 9 scoops and my ph is now at 6.6 but my KH is still at 0.
    My questions are
    How much hight should I take the pH?
    And how do I now Hey the KH up?
    Growing silver perch
    2 grow beds
    Ammonia .25
    Nitrite 0
    Nitrate 160+
    Thanks in advance. .
    Jason



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  2. denandbil

    denandbil Member

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    Country:
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    Victoria
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    Grovedale
    IMO somewhere between 6 and 7 for ph is fine. It is something that is worth checking on a regular basis. When My ph is low, I alternate hydrated lime and eco rose to bring the ph back up.

    I have never worried about or measured KH. Have you got airstones in your FT? I think plenty of air is more important than KH.
     
  3. jassouth

    jassouth New Member

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    Yeah I Have plenty of air.
    I failed to mention that I have tried lime and although it did lift the pH it had a very short effect, hoping by trying to adjust the kh will adjust the buffering and will then control the pH over a longer period.


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  4. Yabbies4me

    Yabbies4me Administrator Staff Member

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    W.A.
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    Perth
    Hi Jason,

    6.5 - 6.8 is a good range to aim for.

    Personally, I would stop testing carbonate hardness and simply focus on raising and buffering your pH to up around that level. Aiming for the top end of that range using the method I've described below should give you a little more buffering and time between doses.

    You have a lot of Nitrates in the system, this is not good for plants, especially seedlings. It can also affect the taste and ultimately the health of your fish. Nitrates at that level would also indicate that there is a lot of Nitrification taking place, this produces natural acids which will be consuming the carbonates in the system, so you are right to be adding some back I into the system to help with buffering the pH.

    However, adding just Potassium bicarbonate will very quickly lead to Calcium and/or Magnesium lock-out. As denandbil suggested, adding both Calcium hydroxide and Potassium bicarbonate is a more desirable approach, but even this is not ideal, as there is a very good chance you still will end up with Magnesium deficiency, or possibly even a Potassium or Calcium deficiency if they aren't added in the correct ratio.

    After much playing around with ratios I've found that the following works best in both raising/buffering pH and keeping the threeway Calcium : Potassium : Magnesium relationship in balance:

    6 parts Calcium Hydroxide, 3 parts pure Potassium bicarbonate, 1 part Magnesium Sulphate...

    So a 6:3:1 ratio

    - At the start of a GB flood cycle I add the Potassium bicarbonate and Magnesium Sulphate (Epsom salts) to the GB, placing it directly underneath the water inflow.
    - I wait for the GB to then complete a Flood & Drain cycle, once it's finished draining I remove the bell from the siphon.
    - Then I add the Calcium hydroxide (completely dissolved in water first) into the GB, again directly under the water inflow.
    - I then allow the GB to run as Constant Flood (bell out of siphon) for about half an hour, then replace the bell.

    I've found that when my system gets down to around 6.0 that 1/3 level teaspoon of Potassium bicarbonate, half that of Epsom salts, and a level teaspoon of Calcium hydroxide raises the pH by around 0.3-0.4... which is about the max you should raise it any 24hr period, but if you were to do it daily you could very quickly get the pH back up around the 6.7-6.8

    That said, your high Nitrates and 0.25ppm Amm suggest your system is overstocked. I would be looking at adding another GB, or reducing fish numbers slightly.

    Cheers!
     
  5. eestrada1234

    eestrada1234 Member

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    Estado de Mexico
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    Hello Yabbies

    Is that ratio per system, or per growbed?
     
  6. Yabbies4me

    Yabbies4me Administrator Staff Member

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    Hi Eestrada,

    I did realise shortly after I posted that a few weeks back that I hadn't included the water volume I was treating, I meant to go back and edit it into the post after I finished another I was writing, but got busy and forgot all about it, so thank you for raising the point.

    The rate and pH rise mentioned, ie: 1/3 level teaspoon of Potassium bicarbonate, half that of Epsom salts, and a level teaspoon of Calcium hydroxide raising the pH by around 0.3-0.4... that was in 500L of water volume in a single IBC system. Always work on water volume in regards to additives for pH buffering/raising.

    The total amount required to raise the pH 0.3 (max recommended for any 24hr period) will vary for each system, depending on the amount of carbonates already in the water, but the 6:3:1 ratio should be pretty closely adhered to unless you start to see obvious deficiency symptoms of one or more of the three elements.

    My system has been running extremely low carbonate levels, and constant low pH levels for some time, so those amounts work for mine at this stage. For someone catching their pH as it declines through the mid 6's for the first time, they may not need as much and should use caution, possibly starting with half those amounts.

    It's all a matter of trial and error, but always err on the side of caution.

    Cheers!
     
  7. Yabbies4me

    Yabbies4me Administrator Staff Member

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    Since replying to this post with the Calcium hydroxide, Potassium bicarbonate, Magnesium sulphate (Epsom salts) ratio, I have considerably altered my approach to raising and buffering pH.

    This was primarily due to a build up of sulphates in the system from the Epsom salts causing issues, mainly with my lettuce, so in place of the Epsom salts I have been using Dolomite lime to provide the Magnesium.

    Following is the list of products I now use to raise/buffer pH while keeping Calcium, Magnesium and Potassium within a reasonable ratio of each other, to avoid nutrient lock-out issues:

    (1). Calcium carbonate (Garden lime, simply crushed limestone)
    (2). Calcium Magnesium carbonate (Dolomite lime)
    (3). Calcium hydroxide (Brickie's lime)
    (4). Potassium bicarbonate

    ...in the following ratio as a starting point:

    6 : 2 : 2 : 1

    This ratio works very well as a starting point, but it may need to be slightly altered at times, depending on the type and number of plants in the system and what stage of their development they are at, ie: growing, flowering, fruiting etc. It's a good idea for growers to educate themselves on the symptoms of Calcium, Magnesium and Potassium deficiency, keep a keen eye out for them, and react early when a deficiency is diagnosed, by altering the above ratio to slightly increase the amount of the deficient nutrient being added to the system.
     

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