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Non-Carbonate Experiment (Clarifications)

Just to clarify.  I didn't want to get too long winded but I have received
some fantastic replies!

Paul Krombholz wrote:
>>R/O water was used to fill each tank, sodium bi-carbonate
>>and trace elements were used to make GH=3dH and KH=3dH

>I don't see how adding sodium bicarbonate could raise the GH

Kent R/O Right was used to get GH=3 (this is what I meant by "trace elements").
Sorry I wasn't very clear there.

Roger S. Miller wrote:
>That's too much of an increase in KH to explain with a small amount of PO4.
>Buffer apparently added from non-RO source is 5 KH - 3 KH, or 2 KH.  2 KH
>is 35.8 mg/l (ppm) as CaCO3.  CaCO3 is 50 mg/milliequivalent, so 35.8 ppm
>as CaCO3 is 0.716 meq/l.  Phosphate is 48 mg/meq as HPO4.  In order to
>provide a 2 KH buffer with HPO4, you would need to add at least
>0.716*48=34.4 mg/l HPO4.  This would work only at pH well over 7.2.  At a
>pH of 7.2 the phosphate would be present as both HPO4 and H2PO4 in roughly
>equal amounts.  The actual phosphate concentration necessary to get the
>2 KH buffer would be twice what was calculated above, or nearly 69 mg/l (!!).

Wow, I wish I could do that.  I'm an EE so I'm limited to circuits and
stuff.  But to respond:  the various types of chemicals in my tap water are
total unknowns.  Maybe there are other chemicals which screw with the pH,
not just phosphate.  I hear that Fort Worth lets the industries dump all
kinds of junk in the water.

>A simple explanation for your observation is that
>the Fort Worth tap water contains something that stimulates photosynthesis
>and is unavailable in your original mix.  You already know that there's
>phosphate (required for plant growth) in it.

Hmm, good point.  That would pretty much flush my results since I assumed
that the CO2 concentration of the two tanks was equal.

Bill Warner wrote:
>please keep in mind that a system like this will never
>actually reach equilibrium.  Depending on how constant your rates of CO2
>addition/loss are, you may reach a steady state condition but this is
>technically not the same as equilibrium.In particular, since the reaction
>	CO2 + H2O --> H2CO3
>is kinetically slow, it is *possible* for the steady state concentration of
>CO2 to be significantly different than would be predicted by simple
>equilibrium calculations.

This is another variable to put into the equation.  The pH of my big tank 
responds to increases in KH like a 3rd order differential equation.
When KH is increased suddenly, the pH jumps and my controller keeps my
CO2 on for 2 days straight.  Eventually the pH will fall and then rise again.
This continues for several days until a steady state value is achieved.

Kinda like a really slow RLC transient response!

Thanks for your comments!

Regan Nantz