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Re: PMDD Dosing System

> From: A M Moore <andy at ascot_u-net.com>
> Subject: PMDD Dosing System
> Is the use of PMDD a complete dosing system or, as I suspect, should we also
> be using nutrient tablets on a weekly/bi-weekly basis as well ??

It should be complete, except for phosphorous.  I get the impression
now that it is possible to drive a tank into a pretty severe phosphorous
deficiency, using this method.  The same arguments we used to account
for the demise of algae (competition with plants for P) then apply
between individual plant species.  In my 160L tank, some plant species
have flourished and others have lost out.  Those that suffered most
have been hygro difformis, alternanthera reineckii and ordinary hygro.
Some plants may also grab elements other than phosphorous at the expense
of other plants.  I have recently been adding small amounts of phosphate
along with the other ingredients, and it does appear to cause a jump
in the nitrate uptake, indicating that the phosphate shortage was
limiting the system. 

> I seem to have been having some nutrient deficiencies recently that are
> slowly going away now that I have started to use the nutrient tablets as
> well as PMDD.

What is in the tablets?  What symptoms have you seen, and on which plants?

The advantage of using a fertile substrate is that the nutrients in it
will stay put (more or less), and the plants don't have to compete with
others a long way away.  If you use a solution-based system, everything
competes with everything else for every nutrient.

Paul Sears        Ottawa, Canada