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> From: Hoa Nguyen <nguyenh at nosc_mil>
> I have a very coarse version of K2SO4.  It was very hard to dissolve and 
> tended to precipitate again from the solution (either that or I was never 
> able to dissolve it that well)
K2SO4 is a booger. I use a 10% solution and that's about the most you
can dissolve. Actually the literature says one gram dissolves in
8.3 ml H2O at 25C, but 1 in 10ml isn't quit as hard, but still hard. 
I make-up a KNO3 and a K2SO4 solution in two different bottles
and use the KNO3 when the NO3 is limited and K2SO4 when I have
~5ppm NO3.
BTW, the max for KNO3 is 35.7g/100ml, I use a 30% solution.

>How much KNO3 should I add to add enough K  to replace the K2SO4? 
>And am I right to assume that the S is not really needed,
>but just there as a carrier?

In KNO3, K is 38.7% of the weight and in K2SO4, K is 44.9% of the weight.
I'll let you do the math because you know what conc. or weights you're using.

> Also, what are the effects of having too much Mg?  Isn't Mg often a 
> component of hardwater?  And if I have hard water, should I still use that 
> much MgSO4?  Is MgSO4 still needed if I use the Microplex trace element mix 
> (it contains 5.4% Mg).

Good question, but you need to know whether the hardness comes 
from Ca, Mg, or a combo of the two. Both analytes are used in 
calc. hardness, but either could also be missing and you'd still 
have hardness (if the numbers are high enough). If you water is 
high in Ca only, I'd say yes, use the MgSO4, but if the hardness 
comes from Mg mostly, then you'll need to add Ca. It's a guess 
until you can find out where the hardness really comes from. Here's 
the formula (minus the Fe, Zn, and other constituents that make-up 
the hardness calculation. They really don't add a lot of hardness, 
especially in our tanks where the conc of these are low to begin 
with.) HARDNESS  = Ca (2.497) + Mg (4.118). You can see where 
Mg at the same level as Ca, would give nearly twice the hardness.

>And am I right to assume that the S is not really needed, but just 
>there as a carrier?

Not really, K2SO4 is a salt, so when it's dissolved, SO4-- is 
present. Sulfate is used by plants, but not the level we use to get 
our K and Mg right. It's overkill, but I don't think it'll hurt the plants 
until a higher conc. is reached. Testing my tanks gives me values 
ranging from 30-200ppm, with the 200ppm coming from my 
Tanganyikan tank, naturally. No plant damage has been observed 
in the years I've been using it.
So, it may help you just to put the trace elements in your PMDD 
and your macro's in their own bottle. It's a lot easier to dose at the 
right levels. In the PMDD, aim for Fe at 0.1ppm, let the rest fall as 
they may, can't do anything about them anyway, and the Ca, Mg, 
and K can be tweeked by themselves. Hope that helps.

Jamie    <"\\\><