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Roger Miller: RO recon
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? 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. 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?
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?). 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? Thanks! Kevin
Department of Herpetology
Bronx, NY 10460
(718) 220 8683 or 5042
Roger S. Miller wrote:
"Gaak! If that's right, then RO Right would give you water with
the composition of dilute sea water, which isn't much at all like normal
fresh water. There's a big variation in the composition of fresh
water, but compared to "normal" fresh water, dilute sea water would
have a high sodium content relative to calcium, magnesium and
potassium and chloride would be high relative to bicarbonate and
We can do better than that. Here's a recipe
Chemical dose/ dose/ measurement
100 liters 50 gallons unit
epson's salt 3.5 6.5 quarter
calcium carbonate 6 11 600 mg tablets
baking soda 4 8 quarter
potassium chloride 1.5 3 quarter
IMPORTANT: I don't use reconstituted RO water and I haven't tried this
recipe in my tanks. Please refer to my first comment to Mr. Malmquist,
above. I do or have before used all of these chemicals for dosing my
tanks. If I go through with my plans to build a solar still, then I'll
probably use something like this to reconstitute the water.
The two recipes are very similar, and designed to produce 3 degrees
of general hardness, 3 degrees of carbonate hardness, about 10 mg/l of
potassium (per recommendation by Dr. Dave some time back), and
of calcium, magnesium, sodium and potassium that I think are reasonably
balanced for growing plants; Ca:Mg = 3:1 and Na:(Ca+Mg+K)<1.
If you reconstitute your water in 50 liter batches (for instance) you
would use half the dosage for 100 liters. If you resconstitute it in 20
gallon batches, you would use 40% of the dosage for 50 gallons, and so
The recipes should be used for water that originally fills the tank and
replacement water used for water changes. It shouldn't be used on water
added to make up for evaporation and it should definitely never be used
a regular treatment to the water in the tank.
A couple years ago Neil Frank, with help from Paul Krombholz and Paul
Sears, posted a wonderful letter on how to dose different chemicals to
different concentrations of important nutrients. I'm pretty sure that
Erik has that letter at thekrib.com. The recipe above is based partly
the information in that letter. It should give the following water
dose/ dose/ measurement
100 liters 50 gallons units
calcium 14.4 13.95 mg/l
magnesium 4.73 4.64 mg/l
sodium 14.24 15.05 mg/l
potassium 11.78 12.45 mg/l
bicarbonate 74.36 75.35 mg/l
sulfate 18.43 18.08 mg/l
chloride 10.72 11.33 mg/l
general hardness 3.13 3.04 degrees
55.7 54.2 ppm as CaCO3
alkalinity 3.42 3.47 degrees
61.0 61.8 ppm as CaCO3
Na/(Ca+Mg+K) 0.44 0.47 molar ratio
total dissolved solids 82.22 83.55 mg/l
The proportion of water in epsons salts varies (see discussion on this
list just a few weeks ago) so the amount of magnesium in this dose will
also vary. If you want to get picky about the details, you could adjust
the epson salt part of the recipe till the GH comes out right, or you
could get an expensive hardness kit that measures calcium and magnesium
hardness separately and adjust the epson salt dose until the magnesium
hardness comes out to 20 ppm as CaCO3.
Also, the recipe calls for using 600 mg calcium tablets as the source of
CaCO3. These are dietary supplement tablets, and they need to be as
nearly pure as you can find - as little color, flavor and binders as you
can get. That probably means the cheapest product on the market. The
tablets should be ground finely. I use a mortar and pestle that my
sister-in-law gave us a few years ago for (I think) crushing spices.
kitchen ware, not lab ware. The CaCO3 will dissolve slowly.
Potassium chloride is most readily available as a no-sodium salt
substitute. In that form it isn't quite pure. I use Morton's "Salt
Substitute" in my tanks. It's about 97% potassium chloride. The
remaining 3% is fumaric acid (harmless, I think) and phosphates. I
to fuss about the phosphates. You can probably get potassium chloride
from a pharmacy or from a nursery, where is might be called "muriate of
potash". The agricultural grade product would probably be impure.
There are some omissions and oddities in the recipe that might give some
There's no silica in the mixture, and silica is usually present in
fresh water at around 10 mg/l. Silica is used by diatoms and some
grasses, but I don't know if any of our ornamental plants need it. If
want silica you can probably get it by adding a little sodium silicate
(water glass). Check for it at your local pharmacy, or maybe even auto
parts store (it used to be used to plug small cracks in engine blocks).
There's no iron, other metals or trace elements of any kind - those
elements will be present as contaminants in the chemicals used for
up the recipe, but not in any known quantities. If you want to add them
you should probably get them from a hydroponics trace element mix.
are dosing instructions in Neil's letter and (I think) elsewhere.
Potassium at about 12 mg/l is higher than is usually found in water as
fresh as this. I can't think of anything wrong with that, and potassium
should be good for the plants, but still it is a little odd.
There's also no nitrate. If you want to add a little then you can
substitute potassium nitrate for some of the potassium chloride. The
information needed to do that substitution is in Neil's letter.
There's no phosphate (unless it comes with the potassium chloride).
That might be a good thing, but remember that your plants must have a
source of phosphate. It's essential.
The pH of the mix will depend on it's CO2 content. You might want to
check that the pH is reasonably balanced before you dump it in your
As always, I'd much appreciate a careful review of these recipes.