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Do I have to dose K2SO4 and how much?

Discussion in 'Aquatic Plant Fertilization' started by dutchy, Mar 9, 2010.

  1. dutchy

    dutchy Plant Guru Team
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    Hi,

    At the moment I'm dosing 8 ppm of KNO3 and 1 ppm of KH2PO4 3 times per week on my 180 gallon tank. How much ppm's K+ does that give me?

    Do I have to dose K2SO4 and how much? On my smaller tank I always got little pinholes iin my Hygrophila Stricta if I didn't dose
    K2SO4.

    Thanks in advance,
    dutchy.
     
    #1 dutchy, Mar 9, 2010
    Last edited by a moderator: Mar 9, 2010
  2. Tom Barr

    Tom Barr Founder
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    Unless you are getting a large amount of N and P from fish waste, there's no need to add extra K, if you use KNO3.
    It gives about a 4X more ratio of K+ to N.
    Adding K2SO4 will not hurt anything either.

    I use it for GH booster mix, but I've not used it for several years without any issues.
    Regards,
    Tom Barr
     
  3. Philosophos

    Philosophos Lifetime Charter Member
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    KNO3 is about 39/101 g/mol NO3, so 8ppm would be about 3.1ppm of K+

    KH2PO4 is about 39/136 g/mol PO4, so 1ppm would be .29ppm K+

    Add those together and multiply by 3 for 10.17ppm of K+ dosed.

    You're a little lean on everything as far as doing goes, though N and P may be coming in from food well enough to stay non-limiting. Try adding about 9ppm of KH2PO4 for a total in the range of 14ppm K+ dosed.

    Personally I'd just increase KNO3 dosing to 10ppm and do something like 7ppm of KH2PO4. Your K+ will come right along with all of it. End result of a weeks dose would be about 20ppm NO3, 5ppm PO4, 17ppm K+ and no risk of deficiencies. I dose more than this and apisto fry make it just fine.
     
    #3 Philosophos, Mar 9, 2010
    Last edited by a moderator: Mar 9, 2010
  4. Wet

    Wet Lifetime Members
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    For clarity, this is incorrect. KNO3 is ~39% K (39g K/101g KNO3), not NO3. KH2PO4 is ~29% K. Your K+ numbers are correct. There is only 1 sig fig here, though. (I mention this because you often times reference the "accuracy" of your methods v other people's method.
     
  5. dutchy

    dutchy Plant Guru Team
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    Thanks all of you for the replies.

    I don't think I'm limiting N, because at the end of the week there's still around 10 ppm of NO3 in the water. So uptake is 25 ppm of NO3 and 3 ppm of PO4 in one week. I dose another 5 ppm of K2SO4 per week to keep the pinholes away. That would mean that the 10 ppm K+ I get from the KNO3 and KH2PO4 dosing is a bit on the lean side for that plant, and it needs more than 10 ppm K+.

    Much clearer now. Thanks.

    regards,
    dutchy
     
  6. Philosophos

    Philosophos Lifetime Charter Member
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