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More on PMDD

Roger Miller wrote:

> > > If you have rising nitrates, then PMDD probably isn't the indicated
> > > solution.

> To which Pat responded:
> 
> > I don't think that I totally agree with this statement. It is possible
that
> > potassium, magnesium or some other element may be in short supply thus
> > keeping the plants from utilizing the available nitrates. Perhaps the
tap
> > water is high in nitrates or the fish load is high. The real beauty of
PMDD
> > is that it can be custom tailored to your needs. The trick is to figure
out
> > what it is you need.

Roger:

> In the absence of any information indicating a deficiency in anything
that
> can be added with PMDD, why would you recommend that Grover use PMDD to
> solve his stated problems?  How should he go about formulating and gaging
> his dose (keeping in mind that iron always reads > 0.1 mg/l with his kit
> in his water and the plants aren't showing deficiency symptoms)?

I believe that Grover's question was more along the line of how to dose
PMDD, rather than how to
solve his stated problem, but here goes. I believe that proper PMDD dosing
should be based on NO3 levels as well as Fe levels. They can, and many
times should, be dosed independently. I'm not suggesting that Grover use
more PMDD. To the contrary, I believe that, for now, he should cut back on
the KNO3 being added. This doesn't mean that he should discontinue the use
of PMDD. He should probably just tweak it some. In Sear's-Conlin Case study
1, K2SO4 was added with the result being a drop in the Nitrate level. I
guess that I read your statement as "If you have high nitrates, then PMDD
is of no use to you". Allow me to quote Sear's-Conlin again. 

   3." A week or so after reaching the target Fe level, check the nitrate
level. If nitrates are below
     about 2ppm, proceed to the next step. Otherwise, add enough K2SO4 to
the tank every day
     to drop the nitrate level to as close to zero as possible and keep it
there (if the nitrates don't
     drop, then something other than K is limiting plant growth and some
detective work will be
     required to find it). Incidentally, measuring the nitrate level is
helpful for general tweaking; if
     adding nutrient X causes the nitrate level to drop, then the tank is
probably deficient in X." 

Grover, read the whole PMDD paper. Roger, I'm just saying that PMDD _may_
be part of Grover's solution, and I wanted to point out that if his current
PMDD formula is not working out the way that he wanted, it _can_ be
changed. There are a great many things that can cause the problems that he
mentioned earlier, and I think that you did a very good job of pointing
most of them out. I just felt like you were selling PMDD short.
 
Pat Bowerman