Re: PMDD - One Month Later (fwd)

---------- Forwarded message ----------
Date: Sat, 14 Dec 1996 9:05:31 PST
From: spush at saudan_HAC.COM
To: Aquatic-Plants-Owner at actwin_com
Cc: rjw at aluxs_micro.lucent.com
Subject: Re: PMDD - One Month Later

> From: rjw at aluxs_micro.lucent.com (Ronald Wozniak)
> 2 Tablespoons of Microplex (5.43% Mg, 0.5% Boron, 0.05% Cobalt, 
> 1.5% Chelated Cu, 4.0% Manganese, 0.1% Mo, 1.5% Zinc, % Fe?)
> 1 Teaspoon of KNO3 (Potassium Nitrate)
> 1 Teaspoon of K2SO4 (Potassium Sulfate)
> added and mixed with 300 ml distilled water.
> Water - Spectra Pure RO filtered Allentown Municipal water
>         KH & GH modified by Baking Soda and PMDD

Ron, are you using straight RO water? Where are your Ca & Mg
coming from? [oops, re-read your whole message and I see you've
realized and corrected this] Those are macro-nutrients. In 
Hoagland's solution the molar ratio of Ca to N is 1:3 and 
for Mg it's 2:15. The "standard" recipe for PMDD has magnesium 
but no calcium. It turns out there might be a good reason for that.

In an article by David Whittaker in TAG 5-2, Mar-Apr 92
titled "Trace Elements" he discusses the stability of three
common chelating agents, EDTA, DPTA and EDDHA. Only EDDHA is
stable at high alkalinities. In TAG 5-3 he expanded on this
to explain that he meant high bicarbonate alkalinity. Apparently
the studies on stability were conducted (by Fischer) under
constant Ca levels of 450 ppm as CaCO3 (but I expect that 
means the method of measuring Ca rather than the use of CaCO3)

Now it wasn't clear to me if it was Ca which displacing Fe
from its chelate, or if the pH was causing the chelate to
become unstable or if the carbonate radical was participating
in a reaction which resulted in the precipitation of iron

The addition of an acid to PMDD will thus help stabilize the
chelating agent in addition to inhibiting fungus and bacteria.
It also gives us another reason to use distilled water not tap
water to prepare the PMDD solution since tap water can contain
lots of Ca and or carbonate.

Incidentally, Dave also commented that EDTA can be used to
chelate both Fe++ and Fe+++. He also said that FeEDDHA is
expensive and rarely used in the commercial trace mineral

Ok, so maybe it isn't a great idea to add CaCO3 to the PMDD
recipe. However Ca is critical to good growth and if your
water lacks it, you may need to add a little limed water once
or twice a week. With steady additions, I've noticed the
Madagascar lace plant leaves have grown larger. I now have
two leaves (mostly stem) that are about 8" in length from a
bulb that was previously all but dormant.

But I am curious. Seachem Flourish has Ca in addition to
Fe. I wonder what they use for a chelating agent?