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trace elements in the substrate [was Re: RO recon]

On Tue, 3 Aug 1999, Steve Pushak wrote:

> You will have an error in calculating concentrations when using
> volumetric measures such as teaspoons and cups, however the target
> concentrations are not at all critical. According to Paul, it makes
> virtualy no difference if say the potassium concentration is 5ppm or 100
> ppm so long as there is a sufficiency.

Of course there is a factor of 20 difference in the cost there, and the
chance of triggering some nutrient *excess* symptoms.  But within
reasonable limits, I agree with this.  The recipe I provided was meant as
a rough starting point from where you could get where you wanted to be,
not as a highly accurate solution.

> To summarize: its ok to use tsps to measure CaCO3, potassium and
> magnesium salts but you should _probably_ use an accurate scale for
> measuring chelated trace nutrient powders.

Of course, for the cost of an accurate scale you might (depending on what
you call accurate) buy a lifetime supply of TMG :)  Also, gain or loss of
water from a powdered preparation can cause the weight necessary for a
given dose to vary over time - sometimes by a lot - so an accurate scale
isn't necessarily the end-all solution.

Are trace elements added to the substrate a reasonable alternative?  I've
heard of people using fritted trace elements; what's the success record
like?  Are there other substrate-bound trace element sources?

Roger Miller