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Re: RO recon
On Mon, 2 Aug 1999, Kevin Zippel wrote:
> On 12 June 1999, Roger Miller posted a great note on reconstituting RO
> water (copied at the end of this message). In this post, he makes
> reference to an earlier post by Neil Frank, Paul Krombholz, and Paul
> Sears, which contained similar info on chemical dosing. I can't seem to
> find the original post -- perhaps it's under a PMDD instead of an RO
> subject line, in which case I'll never find it! Can anyone point me in
> the right direction?
It's at http://www.thekrib.com/Plants/Fertilizers/dosing.html
> One thing about Roger's recreation of the formula
> that confuses me (I'm no chemist!) is how those ingredients can generate
> a GH of ca. 3d. Using recommendations posted numerous times on this
> list, we know that 2 teaspoons of calcium carbonate will raise 13
> gallons by 4d (both KH and GH). Roger's formula requires 6600 mg of
> calcium carbonate (6.6g, approx. 1 tsp) for 50 gal. That's 1/2 the
> chemical dose for 4x the water, or 1/8 the previously recommended dose,
> which would seem to then yield 0.5 d GH.
I don't really know the origin of your dosing advise, but in order for 2
tsp of CaCO3 to create 4 dGh in 13 gallons of water it would have to weigh
1.76 grams per teaspoon, which I think is only about a quarter to a third
of the actual weight of a teaspoon of powdered CaCO3. By my estimates it
would only take something like 1/2 teaspoon of powdered CaCO3 to generate
4 dGH in 13 gallons of water.
You may not be a chemist, but you did a pretty good job of catching a
couple problems I had with calculating the dose from the calcium tablets.
First, the tablets described in Neil's paper contain 600 mg of *calcium*.
I treated them as if they contained 600 mg of *calcium carbonate*. To
contain 600 mg of calcium the tablets would actually contain 1500 mg of
calcium carbonate.
Second, I mishandled the calculation of Kh from the tablets. To be clear
I'll state this precisely; I will assume the CaCO3 is dissolved in water
creating a solution with a high pH and that the solution will be allowed
to react with air or with added CO2 until the CO3-- ions are all reacted
to bicarbonate (HCO3-) ions and the pH drops to more reasonable numbers
(say, below 8.5). My confusion on this point also altered the amount of
sodium bicarbonate needed to make 3 dKH.
> Granted, there is also
> magnesium in the formula (epson salt), which will contribute to GH, but
> clearly less than the calcium (as evidenced by thier final
> concentrations in mg/l, 4.64 vs. 13.95). So where am I losing it?
The magnesium provides about 1 dGH. The calcium should provide 2 dGH to
total 3 dGH.
> Similarly, I don't see how KH can be ca. 3d. We get 0.5dKH from the
> calcium carbonate, plus 2dKH from the sodium bicarbonate (if 1 tsp gives
> 4dKH to 13 gallons, as per previous recommendations, then the 2 tsp / 50
> gallons in this recipe should yield 2dKH, yes?).
According to Neil's paper, a 1/4 teaspoon of sodium bicarbonate weighs 1.3
grams, so a full teaspoon would weigh 5.2 grams (+/-, I'm sure). 5.2
grams of sodium bicarb would give 3.78 grams of bicarb. In 13
gallons of water that's 76.7 mg/l of bicarb, or 3.5 dKH. Two teaspoons in
50 gallons would give 2*3.5*13/50 = 1.8 dKH. Close.
> 2.5dKH is closer to
> the predicted 3 than we got with GH, but still short of the mark. Can
> anyone put me in touch with the original post, Neil Frank, or an error
> in my calculations?
Kevin, thanks for giving the recipes the careful review they need. The
corrected recipes follow.
Chemical dose/ dose/ measurement
100 liters 50 gallons unit
epson's salt 3.5 6.5 1/4 teaspoons
calcium carbonate 2.5 4.5 600 mg tablet
baking soda 2.5 4.5 1/4 teaspoons
potassium chloride 1.5 3 1/4 teaspoons
The composition (after the pH drops) should be
dose/ dose/ measurement
100 liters 50 gallons units
calcium 15.0 14.3 mg/l
magnesium 4.7 4.6 mg/l
sodium 8.9 8.5 mg/l
potassium 11.8 12.4 mg/l
bicarbonate 69.4 66.0 mg/l
sulfate 18.4 18.0 mg/l
chloride 10.7 11.3 mg/l
general hardness 3.2 3.1 degrees
57.1 55.0 ppm as CaCO3
alkalinity 3.2 3.0 degrees
56.9 54.1 ppm as CaCO3
Na/(Ca+Mg+K) 0.27 0.26 molar ratio
total dissolved solids 79.8 78.9 mg/l
And of course, all the same instructions and cautions that went with the
first draft could be repeated here.
One set of comments down. Any other?
Roger Miller