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Re: Reconstituting RO

At the risk of triggering another (ad nauseum) from the list Mom...

Bob Dixon wrote:


> How about dolomite?  It is available 
> crushed from gardening centers, and if we redirect a small amount of CO2 from 
> our aquaria to our mixing "vats" it should dissolve overnight.  Would it not 
> contain the correct, or close enough to the correct, ratios of Ca, Mg, and 
> CO3?  And would CO2 injection even be necessary to get it dissolved at a 
> reasonable rate if we are preparing our water far enough in advance?

If what you aim to do is add general hardness and alkalinity, then
dolomite is probably a better choice than calcium carbonate.  Ideally, it
provides Ca and Mg in the ratio of 5:3 (by weight) and GH and KH in a 1:1
ratio.  Dolomite is often not pure, and the Ca:Mg ratio will increase if
there is any calcite in the dolomite.  Calcite in the dolomite will not
change the GH:KH ratio.

On the slightly down side, dolomite is a little more difficult to dissolve
than calcium carbonate, and I've never seen it available in nicely
preweighed quantities like calcium carbonate tablets.

The recipe I offered wasn't intended just to increase GH and KH, but to
provide a DIY means of reconstituting RO water to get water that resembles
"normal" fresh water in it composition and provides the nutrients normally
required in fresh water in ratios that should be good for growing plants.

If I lose the epsons salt from the recipe in favor of dolomite for
magnesium and alkalinity then the recipe will need some other source for
sulfate.  I'll also have to drop the baking soda out of the recipe, as
that would not be needed to provide alkalinity, and dropping the baking
soda out would leave sodium out of the recipe.

Sulfate (for sulfur) is used by plants, though not in large amounts.
Sulfate is usually common in fresh water so I'd be surprised if plants are
adapted to scavenge sulfate at low concentrations.

Sodium isn't needed for plant growth as far as I know, but it is pretty
much ubiquitous in natural water and I don't feel real comfortable leaving
it out of the mix.  Animals may very well need it for something or other.
> ------------------------------

Write Huntley wrote:

> >In most parts of the US, the effective way to rebuffer the RO water is by
> >just mixing back in some tap water until the desired hardness/buffering is
> >reached.

This is certainly the easiest way to reconstitute RO water.  It gives you
a mix that is just a diluted version of your tap water.  Usually that's

If your tap water is really bad for growing plants (e.g. sodium too high
compared to Ca, Mg, K) or contains some normal component in very small
amounts (K, for instance) then other chemical additions may still be
necessary.  Without using something else to reconstitute the water you
would just be making the original problems worse.

> ------------------------------

James Purchase wrote:

> Regarding your "recipe" for water:
> > 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 teaspoons
> > calcium carbonate 6 11 600 mg tablets
> > baking soda 4 8 quarter teaspoons
> > potassium chloride 1.5 3 quarter teaspoons
> Is this using 1/4 tablespoon measures? (measuring spoons come in sets - 1/4,
> 1/2, 1 Teaspoon, and 1 Tablespoon)

Mmm.  Looks like your mail client stripped the tabs out of the table. That
certainly makes it harder to read.  There should be four columns.

The doses for epsons salt, baking soda and potassium chloride are cited as
the number of 1/4 teaspoons needed:  3.5 quarter teaspoons (for instance)
is 7/8 of a teaspoon.  8 quarter teaspoons is two teaspoons, and so on.  
I used the 1/4 teaspoon as my measuring unit because Neil did it that way.
It seems to be pretty convenient, though perhaps not the most obvious way
of doing things.

Incidentally, my tap water is far from great for growing plants, so I
already add three chemicals to all the water I put in my tanks; sodium
thiosulfate for dechlorination, potassium chloride and epsons salt.  The
difference between my normal procedure and DIY RO-water reconstitution
(which requires only 4 major chemicals) is so small that I wouldn't need
to be very upset about the commercial alternatives before deciding to do
it all myself.

But I'm like that.

Roger Miller