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Re: Exceeding saturation points

Rod wrote:

> I'm not a chemist, nor even much of a mathematician.
> However, purely as a matter of logic, if you have two
> or more solutions which are below the saturation point
> of some particular solute, adding those solutions together
> can never cause the solute to exceed the saturation point.

That's true as long as both solutions contain the same solutes.  If they
contain different solutes then the combination may form compounds that
will precipitate or react.

As a hypothetical example, say one solution contains a phosphate, but no
calcium, and that a second solution contains calcium but no phosphate. 
If you mix the two then a calcium phosphate should precipitate.

Another case might occur if one solution were stabilized by a low-pH
buffer, and the other solution stabilized by a high-pH buffer.  A
mixture of the two will probably give you a pH that is either high or
low--it can't be both.  Some of the constituents will be unstable at the
final pH and may precipitate.

I can't say that either of these cases (or any other example) would
actually occur in mixtures of fertilizer solutions, but they are
certainly possible.  Generally, you probably shouldn't mix
commercially-formulated fertilizers.  You might get away with it, or you
might not get the result you want.

Roger Miller