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Re: Aquatic Plants Digest V3 #213

Andrew Claxton wrote:
> Date: Sun, 19 Apr 1998 09:46:09 -0700 (PDT)
> From: Andrew Claxton <aclaxton at yahoo_com>
> Subject: PMDD and MgSO4
> I am still confussed as to what the MgSO4.7H2O is in the PMDD.  I have
> straight MgSO4 from Homegrown Hydoponics.  Will this work or should I
> buy epsom salts?  Will any epsom salts work or are only some fully
> hydrated?  The epsom salts at my local pharmacy are not labelled.
> Also does any ony know of a place to get the Lamotte test kits in Canada?

Hi, Andrew,

Magnesium sulphate is magnesium sulphate. The water of hydration is
significant ONLY on the crystalline (dry) form. Once you put magnesium
sulphate in water it will become a magnesium sulphate SOLUTION,
regardless of which starting material - MgSO4, MgSO4.H2O or MgSO4.7H2O -
you used. The PROPORTIONS, however, have to be changed, if you are
following a recipe:

For each 1 gram (or ounce) of MgSO4 you have to use 2.0 grams (or
ounces) of 7-hydrated magnesium sulphate (Epsom salts, MgSO4.7H2O).
Sorry, but "tablespoons" can not be so converted! (Well, they can, but I
do not have the necessary bulk density data!)

I do not know what form of magnesium sulphate they use in hydroponics.
To be safe, use Epsom Salt, although I don't think that magnesium
content is very critical. You can look at the crystals in your
hydroponic salt and Epsom salts. If they look very much alike, they
probably are, because Epsom salts is about half the price of the
anhydrous stuff (MgSO4).