Just to get my head around this...... PO4

Discussion in 'Aquarium Fert Dosing' started by AndyOx, 3 Nov 2009.

  1. AndyOx

    AndyOx Member

    Messages:
    87
    Location:
    South Oxfordshire
    Now I'm gonna do the speed version of this question, but feel free to answer at whatever length be appropriate!!

    Natural PO4, that which arises from fish feeding, waste, natural decay etc is this a different form of PO4 than the dry salt I use? Or is it that one favours algae growth more than plant growth or is easier for plants to assimilate?
    I understand that the PO4 I add is very much a friend and the other is not :lol: I'm just curious as to why?

    Cheers :?
     
  2. roadmaster

    roadmaster Member

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    I wonder why one would buy powder when natural process provides it for nothing? How much powder is too much?
     
  3. JamesC

    JamesC Member

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    1,276
    Location:
    Bexley, Kent
    There are three types of phosphates - orthophosphates, polyphosphates and organic phosphates.

    Orthophosphates are what we add to our tanks and farmers put on their fields.
    Polyphosphates are metal ion complexed phosphate that are used in things like detergents.
    Organic phosphates are organically bound phosphates which are used for things like pesticides and also come from animal poo and also food.

    Depending on where we live our tap water contains orthophosphates and polyphosphates in differing concentrations. There should be very little in the way of organic phosphates. Plants (and algae) can use orthophosphates and also possibly polyphosphates. I'm not sure though if plants can use the polyphosphates directly but they undergo hydrolysis in water and are converted to orthophosphates which are the plants preferred source.

    James
     
  4. roadmaster

    roadmaster Member

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    What are Orthophosphates comprised of ? I am keenly interested in the benefits of this particular type of phosphate over organic phosphates. Have expierienced the effects of the latter in low tech planted aquaria but have been up to this point ignorant of the orthophosphates you speak of.
    How has it been determined that plants prefer one over the other and please excuse admitted ignorance. :oops:
     
  5. JamesC

    JamesC Member

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    1,276
    Location:
    Bexley, Kent
    Wikipedia is your friend - http://en.wikipedia.org/wiki/Phosphoric_acids_and_phosphates. Basically salts like potassium phosphate are orthophosphates.

    Doing a Google search brought up loads of articles on the different types of phosphate and plant uptake. Here is one such article - http://www.water-research.net/phosphate.htm. Plants only use orthophosphates but in water polyphosphates hydrolyse to orthophosphates so are used at this point. Organic phosphates also decompose eventually to orthophosphates. If you want to fertilise your plants then I would suggest to use an orthophosphate.

    HTH
    James
     
  6. roadmaster

    roadmaster Member

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    Thank you much! The second site suggested provided the precise info I was looking for in apparently the wrong places.
    I am now wondering ,at what levels in a closed sytem, would these phosphates be considered potentially harmful to fish. I will assume that frequency and volume of water changes would help in that respect but can find no consensus beyond some studies with game fish,as to what levels would be considered detrimental to longterm health and or reproduction in tropical fish. I ask this for I am contemplating going from what most would consider low tech to CO2 injection but the Discus and Rams that I presently care for have demonstrated a marked decline in successful spawnings with nitAte levels much over 20ppm. This precipitates that I perform a couple water changes per week. My fish are healthy and producing young which I am able to sell to offset my expenses and I am not inclined to make things more difficult if I can help it. At the same time, I have been looking at the beautiful planted tanks here and elsewhere and hence,my query with regards to phosphate dosing in particular.
     
  7. ceg4048

    ceg4048 Expert/Global Moderator Staff Member

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    8,953
    Location:
    Chicago, USA
    I've had planted tanks extremely high in inorganic PO4 and inorganic NO3 with no effect on breeding performance. The mis-correlation occurs when we assume that organic forms of these components are toxic. If your tank is high in organic species of NO3 then the damage has already be done by what the NO3 started off as - typically ammonia or other forms of nitrogen bound in organic waste content such as proteins and so forth. The end product is NO3 but this is not what does the damage. The same can be said of PO4. If it's origins are organic, such as food, decaying vegetation, or feces, then it's release into the system is a result of Redox reactions which lower oxygen levels, for example, in order to breakdown the components. Organic PO4/NO3 are merely the smoking gun. This is why water changes are so important in a CO2 injected tank. Not to remove NO3/PO4, but to remove their detritus/waste product origins which are highly toxic. High CO2 equals high growth rates which generates high levels of organic waste. So it's as simple as keeping the tank scrupulously clean. Then you will see that it is not the NO3/PO4 levels that are relevant, but merely the reduction of organic waste from which they originate.

    Inorganically dosed NO3/PO4 are greener and cleaner simply because they do not require breakdown and extraction from toxic components. They are immediately available, have little effect on Redox potential and have minimal toxicity. Inorganic salts added to the tank do however sharply increase the Conductivity (Total Dissolved Solids) and therefore, if the breeding fish are sensitive to TDS then this will be an issue, but again, it has nothing to do with toxicity.

    Cheers,
     
  8. roadmaster

    roadmaster Member

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    Thank you for the informed response. Me thinks I need to do some more research. ;)
     

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