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Re: peat and hard water

Toan wrote:

> What possible methods are there to reduce water hardness?
> I know two; deionization and reverse osmosis. are there
> any other ways of reducing hardness?

Ion exchange is the normal method.  Commercial softeners usually use
zeolite as an exchange medium.  Some small-scale softeners and deionizers
probably use special polystyrene beads.

> I'm still very
> confused on the subject of water hardness -- the scales,
> the types of hardness -- despite my efforts to understand
> it.

The aquarium literature is pretty confusing, because some authors use
"hardness" to describe several different things.  They also use several
different ways of measuring it, so your confusion is understandable.

In technical literature "hardness" measures the concentration of
calcium and magnesium (along with some relatively rare elements).  That's
what the aquarium literature usually calls general hardness or total

The actual units used to measure hardness are confusing, even in the
technical literature.  The simplest and most common measure is "mg/l as
CaCO3".  Expressed that way, the numbers give the amount of the mineral
calcite (CaCO3) that you would have to dissolve in the water to make that
much hardness.

There are other measures.  In the hobby we often use the German degree.
There's also an English degree (also called a Clarke) and grains per
gallon, which can be called an American Degree.  "Degrees" of hardness
provide lower numbers that are easier for qualitative thinking.  You
can get them directly from hardness as mg/l CaCO3 with simple
conversions.  For instance, hardness in German degrees is equal to
hardness as mg/l of CaCO3 divided by 17.8.

The term "hardness" is widely abused.  Lots of authors in the hobby use
the term "carbonate hardness" to describe buffering capacity.  To make
things worse, vendors of test kits sold in the hobby seem to like that
term too.  In technical literature buffering capacity is called
"alkalinity".  There is a lot less potential for confusion if we use
"alkalinity" rather than "carbonate hardness".

In both the hobby and in technical literature we use the same units to
describe alkalinity that we use to describe hardness; i.e. mg/l as CaCO3,
German degrees, and so on.  Alkalinity almost always measures the
concentration or bicarbonate, so when we express it as mg/l as CaCO3 the
value is the amount of the mineral calcite (CaCO3) that we would have to
dissolve in water to create that much alkalinity.

There are other problems.  Sometimes "hardness"  is used to describe the
total mineral content of water.  Even worse, some people (water treatment
vendors are really bad at this) will mix and match hardness terms and use
it to describe anything and everything they feel like.  I once heard a
salesman refer to "sodium hardness" and "arsenic hardness".

> I recently read that the addition of peat would render
> the chart many people use to determine CO2 concentration
> by measuring water hardness and pH to be inaccurate. This
> makes sense, because peat moss only lowers pH and not
> water hardness... doesn't it?

We don't measure water hardness and pH to determine CO2; we measure
*alkalinity* and pH.  See the preceding discussion on how "carbonate
hardness" is a confusing term that we should avoid using.  I don't know
that peat will invalidate the alkalinity - pH relationship for CO2.

The actual effect of peat on water chemistry can vary a lot.  Peat (and
other stable, soil-derived organics) have some cation exchange capacity
(sometimes a lot of cation exchange capacity). A cation exchanger pretty
much always has something occupying its exchange capacity. If it has
calcium and magnesium occupying its exchange capacity when you use it,
then it will not soften your water - it can make it harder.  If it has
hydrogen occupying some or all of its exchange capacity then it will
soften your water by trading hydrogen ions for calcium and magnesium ions.
In that case it might also make your pH crash.  If it has ammonium in its
exchange sites then it may soften your water, but release ammonium into
the water.  If it has aluminum occupying the exchange site, then it might
release the aluminum and kill your plants.  In this latter case I don't
recall whether it will soften your water or not.

Fortunately, the peat that is commonly sold in the aquarium hobby doesn't
usually have the bad side effects.  Some sold in the gardening trade is
sold to lower soil pH and it will lower your aquarium pH as well.  Some is
treated with lime so that it won't lower the pH, but in that case it won't
soften your water either.

Peat, just like any other cation exchanger, has a limited capacity to
soften water.  After a while it just comes to a balance with your hard
water, and the softening stops.  If you want to keep using it to soften
water then you have to change it out every now and then.

Roger Miller