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The Optimal KH & GH Range for Growing Plants

Discussion in 'Are you new to aquatic plants? Start here' started by Chunks, Jul 20, 2012.

  1. Chunks

    Chunks Prolific Poster

    Oct 5, 2011
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    7:41 PM
    I though that I would raise this topic so that it can be settled once and for all. I have been doing extensive research on this subject and most of the answers contradict each other or don't provide hard evidence as to what is scientifically proven. Or even worse they just say put a bit of GH Booster in with your water change... there are a number of problems with this, what if you have very soft water or very hard water. If you already have very hard water you don't need a booster but could you perhaps need to soften the water in order to get optimal plant growth? If you have very soft water then a "bit" of GH booster may not be enough in fact you could still have a deficiency. So lets settle this what are the optimal ranges one should aim for. I have heard figures from a minimum of 4dGH or ranges from a minimum of 6dGH to 12dGH. For KH i have read that the optimal range is between 4dKH to 8dKH. So what is the correct range for optimal plant growth.

    This post is part education and part question so that future users of this website with the same question can find a definitive answer.

    GH or General Hardness
    This is essentially a measure of the calcium (CaSO4, Gypsum) and magnesium (MaSO4, Epsom Salts) levels in your water. Most tap water will contain a degree or two of GH already (or in some areas it may contain larger amounts) and is easily measured with a water test kit for KH/GH (often sold as a pack together in your local fish shop LFS). If your using rain water or RO/DM (Reverse Osmosis/De-mineralised) water then your GH will be very low/nothing especially in the case of RO/DM as this process effectively strips out all minerals and metals leaving you with "pure water". This however has to be re-constituted to be of any real use in sustaining life.

    - Effect of low GH on Plants.
    A Magnesium deficiency can be identified by leaves with darker veins while the surrounding leaf tissue is lighter in color.
    A Calcium deficiency can be identified by leaves with small twisted pale new growth. (This could also be caused by an over dose of Potassium (K) or Magnesium (Mg))

    KH or Carbonate Hardness
    Carbonate hardness or carbonate alkalinity is a measure of the alkalinity of water caused by the presence of carbonate (CO32-) and bicarbonate (HCO3-) anions. It is usually expressed either as parts per million (ppm or mg/L), or in degrees KH (from the German "Karbonathärte"). One German degree of carbonate hardness (dKH) corresponds to the carbonate and bicarbonate ions found in a solution of approximately 17.848 milligrams of calcium carbonate (CaCO3) per litre of water (17.848 ppm). - Wikipedia answer

    - Effect of Low KH on Plants
    KH effects the PH buffering ability of your water. The optimal/ideal PH for plant growth is said to be 6. The PH value influences your plants ability to take up nutrients. So if your water has a low/high KH your plants may indirectly suffer because of not being able to absorb the available nutrients. The PH/KH value can be adjusted UP easily by using Sodium bicarbonate (NaHCO3, Baking Soda), this only has an affect on your KH and not your GH. It's more difficult to lower you PH level, it can be done by using a reverse osmosis filter, it effectively resets your water so you can start again. Plants are quite flexible to the PH range (with in reason) most doing reasonable well with a PH of 6-7. Some species requiring softer water and some harder.

    So the reason for this post is to set a dGH and dKH range to aim for. I don't know that answer so thats where the knowledgeable Plant community comes in. Also please correct any mis-information that may exist so that no further mis-conceptions spread.

    What is the optimal GH range?
    - What is the minimum GH?

    What is the optimal KH range?
    - What is the minimum KH?
  2. gomgom

    gomgom Prolific Poster
    Lifetime Member

    Nov 8, 2011
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    7:41 PM
    In all my tanks, 8 , all are very planted, i keep kh under 3 in shrimp tank, others are kh under 1. I dont care about gh, just watching tds once a week

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