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Re: Hoagland's Solution

    * From: "David A. Youngker" <nestor10 at mindspring_com>

...Also, my thanks to Paul Krombholz of the ever meterologically-interesting
Mississippi for jarring my memory on, of all things, Hoagland's Solution. My
local water here in Chattanooga (as Tom Barr and others will attest to after
AGA conference) usually only needs a touch of calcium, magnesium and
potassium to be prime, but takes a _load_ of iron to do the plants justice.
Much as I'm fond of SeaChem's Flourish Iron, I can usually formulate
concentrations that are more handy to me personally if I go DIY. The mere
mention of Hoagland's reminded me that *chelated iron* is usually a
stand-alone addition to the solution just prior to use. It didn't take long
for me to come up with about 4 different variations on the iron portion.

Now I can't get my hat off my head!  I was reminded that I was asked what
the composition of Hoagland's solution was, and life got a little busy just
then, and Tom Barr came in with a formula  before I did.  Tom's formula was
different than the one I used:

From Tom Barr:

> Looking at the solution and the compounds that make up the solution I see
> that KNO3 is the main source of N but the ratio of NH4 to NO4 is about 1.75
> NO3 to 1 NH4. (Source: Epstein 1972)

> KNO3:         1M 6.0mls            N  224ppm
> Ca(NO3)2*4H2O 1M 4.0mls            K  235ppm
> NH4H2PO4      1M 2.0mls            Ca 160ppm
> MgSO4*7H2O    1M 1.0mls            P   62ppm
                                     S   32ppm
                                     Mg  24ppm

The formula I used in the '60s (Hoagland and Snyder, 1933) was as follows:

KNO3            1M  5.0mls            N  210 ppm
Ca(NO3)2*4H20   1M  5.0mls            K  235 ppm
MgSO4*7H20      1M  2.0mls            Ca 200 ppm
KH2PO4          1M  1.0mls            P  31  ppm
                                      S  64  ppm
                                      Mg 48  ppm

When growing the aquatic plants I used 1/5 the above concentrations plus
micronutrients plus iron EDTA.  The plants grew very well for me in the 1/5
Hoaglands.  Compared to the more recent formula (Epstein, 1972) this
fromula has no ammonium, twice as much sulfur and magnesium, and half as
much phosphorus.   Species that I grew successfully included Ceratophyllum
demersum, Vallisneria americana, Zosterella dubia, Elodea occidentalis, and
Aponogeton madagascariensis.

Iron EDTA did not keep well in the nutrient solution.  Light and phosphate
precipitated some of the iron out.  I had to play a balancing act between
the iron and the phosphate levels.  That was the main reason why I settled
on 1/5 strength Hoaglands.  If I tried 1/2 strength, I had a lot of iron
precipitated out by the higher phosphate levels. Besides, I got enough
growth to pretty much fill the flask with plants with the 1/5 strength.
Today, we have better chelating agents available, such as DPTA, which is
much more stable and lasts for weeks in the aquarium.

Paul Krombholz in warm, humid, central Mississippi, with a record high of
83 F. today and then some strong evening storms with gusts to 50 mph and
some trees down.