re: PMDD component stability

---------- Forwarded message ----------
From: psears at emr1_NRCan.gc.ca (Paul Sears)
Message-Id: <9701211938.AA17137@emr1.emr.ca>
Subject: Re: PMDD component stability
To: Aquatic-Plants at ActWin_com
Date: Tue, 21 Jan 1997 14:38:26 -0500 (EST)

> From: James Wong <u2120863 at acsusun_acsu.unsw.edu.au>
> Subject: Precipitation of chemicals other than Fe
> I have a dumb question for the chemists on the list.

	Not dumb at all...
> My question is do the other chemicals in the PMDD mix precipitate out of 
> solution or degrade prior to their addition into a fishtank? If so which 
> ones and under what conditions?

	Mg++, K+, NO3-, SO4--   Not at all, and not in the tank either.
	Mn, Cu, Zn, Fe as chelates should be chemically stable, but
liable to attack if kept in light, and probably liable to bacterial
/fungal? attack as well.
	MoO4--, B(OH)3 should be stable, though the MoO4-- may (slowly)
attack the chelating agent on the first four metals.
> I ask this becasuse I'm thinking of making my next batch of PMDD with the
> Fe solution seperate from the rest of the ingredients

	It would certainly be O.K. to make up and keep a solution of
the MgSO4(12? H2O), KNO3 and K2SO4, probably for years.
	I'll take this opportunity to mention the fact that the idea
of the original posting in which "PMDD" occurred was to explain a
_method_ for algae control, not just a recipe for a fertilizer.

	The idea is that most planted aquaria are short of potassium
and trace elements, so add them.  The plants can then use any nitrogen
available, so the nitrate concentration will start to fall (if there was
any to start with).  Add enough nitrate to keep a few ppm in the water
Adding magnesium is usually a good idea too.  If the algae don't give
up over a few weeks, add more potassium.  This is the one thing we can't
easily measure, but I find that algae outbreaks are usually accompanied
by holes in older leaves, and both stop when more potassium is added.
I find that hygro shows the K shortage first.

Paul Sears        Ottawa, Canada

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