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Re: Altering tapwater chemistry with peat

> Date: Thu, 28 Sep 2000 21:15:47 +0100
> From: "wayne swaby"

> A letter which recently appeared in a UK fishkeeping
> magazine advocates the use of Irish Moss Peat from
> the garden centre as a means of altering the chemistry
> of tap water to make it favourable for growing plants...He
> claims that pH drops from 8.3 to 5, and KH from 13 to 3.
> He then adds untreated tap water to get his desired
> parameters.
> I can see how pH would be reduced by the (humic?)
> acid contained in the peat, but can someone explain
> what brings about the change in hardness?...

Some peats have a limited ion exchange capability. In addition to outright
releasing acids, some of the compounds will exchange hydrogen for calcium or
magnesium in situ. This will affect your GH to a small degree.

But the alkalinity (KH) is exhausted strictly through the release of acidic
organics. Putting an excess of available hydrogen in the water will cause
the carbonic chain to move toward the CO2 end of the reaction, dissipating
CO2 and leaving water behind.

> ...Can anyone say anything for or against this method?
> I'm currently getting together all the stuff for my first
> serious attempt at a high-ish tech planted tank and will
> gratefully accept the 200 saving from not buying an
> RO unit if its any good.

An RO or DI unit is most cost- effective for removing General Hardness -
calcium, magnesium and iron compounds *outside of* carbonates. It also
removes most of the rest of anything dissolved in the water, such as "table"
salt, organics, etc. Alkalinity is too easily adjusted *without* using these
as the primary approach. They're also good if your alkalinity is on the very
high side, because boiling or acidifying the water to remove the carbonates
will still leave ionic calcium/ magnesium compounds. If your water's not so
high, it's not a major concern. (That would be something like "liquid rock"
and 300 - 400 ppm alkalinity - Lake Tanganyika - as opposed to most normal-
range tap water.)

> ...By the way, my tapwater has a pH of 7.4, I havent got
> around to measuring the KH yet, but I figure its going to
> be higher than ideal...

Are you sure it's too high? Most people who supplement CO2 usually shoot for
a KH that gives them mid-7 pH ranges so that the CO2 will drop the tank to
about the 6.8 range or so.

If you don't have the test kits, it may prove very worthwhile to either take
some samples to a dealer that will test it for you, or call your local water
utility to ask about the chemistry.

Odds are, you *might* not have to do _anything_. So, the question

> Are my chances of success going to be seriously hampered
> if I use the tapwater with nothing but a bog standard water
> conditioner like stress coat?

could very likely point to saving money on your part.

As to the efficacy of peat- treated water for *plants*:

It's been theorized that the organic compounds released through vegetative
decay in natural bodies of freshwater do far more good for the plants than
for the fish. They seem to provide the main body of chelating agents for
nutritional prep work, and other than acidifying the water don't seem to do
a whole lot else. I would think that if you're going to provide additional
nutrition through fertilization, it's better to add a few drops of something
like Flourish than to dump, say, some nails in the tank, peat treat the
water and hope enough of the iron gets converted  ;-)

If you're interested in the generalized effect of peat on GH and alkalinity,


for some studies I started but haven't yet finished...


David A. Youngker
nestor10 at mindspring_com