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Insolube substance in hydroponic nutrient solutions

Insolube substance in hydroponic nutrient solutions - Chemistry Forum

Insolube substance in hydroponic nutrient solutions - Chemistry Forum. Discuss chemical reactions, chemistry.


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  #1  
Old 10-08-2003, 09:54 PM
Repeating Decimal
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Default Insolube substance in hydroponic nutrient solutions



I am using a bloom formulation nutrient solution for my tomatoes marketed by
Grow More. According to the label, it is supposed to be completely water
soluble. Nevertheless, I find a residue thaat appears to be insoluble.

It is white. It seems to form large particles about one mm across. Adding
dilute (circa 10%) sulfuric acid to it does not dissolve it. Reading over
the list of incgredients, the only thing I can think of that is relatively
insoluble is calcium sulfate. It is soluble enough so it should not be left
over. Resh (hydroponics author) says one part calcium sulfate will take 500
parts of water to dissolve. If so, it does not dissolve easily. It could be
produced from calcium salts interacting with sulfates.

Has anyone else seen that? Does anyone know what I am observing? What else
can it be? What is a simple test for gypsum (calcium sulfate)?

This is mixed with fairly hard (Ca, Mg), slightly alkaline tap water about
pH 7.3. The result is slightly acid, about pH 6.8 although it drops after
being depleted by plants.

Besides calcium sulfate, what elese could be precipitated out?


The listed ingredients are:

Ammonium phosphate
Ammonium nitrate
Potassimum phosphate
Potassium nitrate
Potassium sulfate
Magnesium nitrate
Calcium nitrate

Trace elements are derived from

Boric acid
Cu, Fe, Mn, Zn EDTA
Sodium molybdate


Bill

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  #2  
Old 10-08-2003, 10:58 PM
Steve Turner
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Default Insolube substance in hydroponic nutrient solutions

Repeating Decimal <[Only registered users see links. ]> wrote:


Calcium sulfate seems a reasonable guess for what you have, IMO. It
is not very soluble in water and is slow to dissolve even to the small
extent that it does.

The solubility is high enough, however, that a saturated solution
should give a precipitate with barium. Take some of your granules and
let them stand in *distilled* water for a couple of days, with
occasional shaking, then add BaCl2 solution to a sample of the
supernatant. Cloudiness or precipitate indicates sulfate or
carbonate. Add HCl to differentiate between the two. If the
precipitate remains, it's sulfate, and the only cation that you list
which would form a poorly soluble sulfate is calcium.


Try dissolving your nutrient in distilled or deionized water. I'm
guessing you won't see the residue.

Steve Turner

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  #3  
Old 10-09-2003, 04:37 AM
Repeating Decimal
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Default Insolube substance in hydroponic nutrient solutions

in article [Only registered users see links. ], Steve Turner at
[Only registered users see links. ] wrote on 10/8/03 3:58 PM:


Thanks for your reply. You suggest the route that I was thinking about.
Unfortunately, it is very difficult, although not impossible to get retail
quantities of reagents around here. Triess sciences in Burbank is one place
I can probably get barium chloride,

The other thing I was thinking of using more readily available agricultural
chemicals. I would mix the nutrient in water. If a precipitate forms, I
would decant some of the solution. Then if I add calcium nitrate solution to
it, it should form a calcium sulfate precipitate with excess sulfate in
solution. If it does not, I have to look elsewhere.

Bill

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  #4  
Old 10-09-2003, 10:09 PM
Steve Turner
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Default Insolube substance in hydroponic nutrient solutions

Repeating Decimal <[Only registered users see links. ]> wrote:


They should sell it; they have in the past. Obviously barium nitrate
would also work and might be marginally easier to find, since it's
used in pyrotechnics. TriEss's traditional minimum quantity of 2 oz
will last you a lifetime of tests for sulfate.

On a more general level ... is sulfate really necessary for a
hydroponic nutrient solution? In other words, is sulfur a
macronutrient for plants, and if so does sulfate ion supply it in
usable form? If not, why even add sulfate? I realize that you're
using a proprietary nutrient formulation, but if you don't need
sulfate you might be able to concoct your own nutrient solution which
remains soluble in hard water.

Steve Turner

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  #5  
Old 10-10-2003, 03:29 AM
Repeating Decimal
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Default Insolube substance in hydroponic nutrient solutions

in article [Only registered users see links. ], Steve Turner at
[Only registered users see links. ] wrote on 10/9/03 3:09 PM:


Yes. Sulfur is a required element. It is usually made available in the form
of Epsom salts. Sulfuric acid is also often used to control pH.

I don't think that the formulation is very proprietary. The label list the
amount of each element and how it is supplied. Sometimes there may be
several sources of the element.

As I thumbed through Resb's book, as close to a hydroponic bible as you can
get, all sulfur is suppled by sulfates. Many trace elements are also
sulfates.

Bill

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  #6  
Old 10-10-2003, 01:38 PM
Steve Turner
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Default Insolube substance in hydroponic nutrient solutions

Repeating Decimal <[Only registered users see links. ]> wrote:


Okay. So it begins to sound like an irresolvable conundrum: the
plants need both Ca and SO4, yet CaSO4 is "insoluble."

Certainly the answer is that the concentration of these ions necessary
to support the plants is lower than the concentration at which CaSO4
precipitates. This is not hard to believe. The CRC lists the
solubility of CaSO4 in water at around 2 g /L, which seems to be in
the right ballpark for a macronutrient. (I could be entirely wrong
about this; I'm way out of my league here...)

This solubility characteristic may provide an opportunity: how about
supplying the necessary Ca and S to the plants by incorporating a few
percent granular gypsum in your hydroponic support matrix? This will
maintain a constant supply of those elements to the plants. Your
nutrient solution would then need contain only N, P, K, and other
trace elements, with no problems with solubility even in hard water.

Steve Turner

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  #7  
Old 10-10-2003, 05:14 PM
Thomas Lee Elifritz
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Default Insolube substance in hydroponic nutrient solutions

Repeating Decimal <[Only registered users see links. ]> wrote in message :


Calcium sulfate and/or calcium phoshate. It is important to keep the
ph slightly under 7 to prevent this.


Wrong, ammonia is unnecessary. Use nitrates.


Wrong, ammonium is unnecessary.


Great, slightly expensive, available in monohydrogen and dihydrogen.


Great, it used to be available in drugstores.


Ok, price is coming down from a new process, don't use too much.


Somewhat expensive and redundant, Magnesium is necessary in low
concentration.

Use magnesium sulfate. It's cheap, available in drugstores as a
hydrate.


Whatever happened to Dr. Chartelier?

Very inexpensive but slightly nasty. Very hydroscopic. Don't use too
much, this is the compound that is causing your precipitate, as it is
the primary nitrate source. Make up the balance with potassium
nitrate.

Cheap, available in drugstores.


Don't use the chealates. Sulfates are much cheaper and non-toxic. Just
watch your Ph.


or Molybdenum Chloride. Also Cobalt Chloride in very trace amounts.

One of these days, I'll get around to posting ppm's quantities and
calculations. In the meantime read anything by Abram Steiner in the
literature. These nutrients form triads :

Potassium - Calcium - Magnesium

Nitrate - Phosphate - Sulfate

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[Only registered users see links. ]

Thomas Lee Elifritz
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  #8  
Old 10-10-2003, 06:08 PM
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Default Insolube substance in hydroponic nutrient solutions

in article [Only registered users see links. ], Steve Turner at
[Only registered users see links. ] wrote on 10/10/03 6:38 AM:


The 2 g/L you refer to is 2000 ppm. That is about most concentrated solution
recommended for ALL the nutrients put together.

Gypsum is often used as a soil conditioner, for that a small but finit
solubility is desirable.

Bill

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  #9  
Old 10-10-2003, 09:16 PM
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Default Insolube substance in hydroponic nutrient solutions

in article [Only registered users see links. ], Thomas Lee
Elifritz at [Only registered users see links. ] wrote on 10/10/03 10:14 AM:


<snip>


I was just listing label ingrfedients, not putting together my own
formulation.

Bill

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