Re: pH vs. TDS

[Mike & Diane Wise <apistowise@fgn.net>]

JerrCarol@aol.com wrote:

> In a message dated 6/26/2002 11:45:55 AM Eastern
> Daylight Time, apistowise@fgn.net writes:
>
>
>
>> For me, with tap water with a KH of 1.5º, the
>> increase in conductivity is almost
>> negligible. For people with really hard water,
>> the pH can only be lowered by
>> removing carbonate hardness. This will require
>> more acid than in soft water, and
>> the increase in conductivity is not a good
>> idea. HCl doesn't increase the TDS
>> very much because chloride ions are not a
>> strong hardening agent. Chloride ions,
>> however, will raise the electrical
>> conductivity considerably. I wouldn't suggest
>> using HCl to lower pH without checking to see
>> what it does to your conductivity.
>> For most soft water fish, increased
>> conductivity is just as detrimental as high
>> hardness.
>>
>> Mike Wise
>
>   Okay Mike,
>   now you got me thinking here.
>
>   Now my understanding TDS is a Total of
> dissolved solids (Calcium, and stuff like that)
> I was also under the impression that the TDS
> took into account the total Carbonate hardness
> and general hardness.

Technically, that is correct.

> Now I understand that the reading on the meter
> when it say 0 is a virtual 0 and not actual but,
> as close as can be depending on the quality and
> calibration of the meter you use. Does this mean
> that when reading 0 you could still have a high
> conductivity reading?

If you want to know the truth, TDS meters measure
electrical conductivity, not total dissolved
solids! There is no real difference in the
electronics in a meter that measures TDS in ppm or
electrical conductivity in µS. In naturally
occurring fresh water, there is little difference
between the 2.

>   And how does one deal with the stats in most
> Apisto books which say the readings are usually
> very low like less than 1?

They use chemical dye tests for these tests. This
is why they often show both GH (total hardness),
KH (carbonate hardness), and electrical
conductivity. This is why conductivity can vary
greatly from the TDS (hardness) in the same
samples

>   What pH would their water be and where would
> the alkalinity or acidity come from?
> I would suppose some would have to be from the
> water running down rocks and leaves and trees
> and stuff like that but, just my imagination.
> Just curious to see what your thoughts are here?

OK, you asked for it. Most of South America is
underlain by granitic & volcanic rocks, at least
where our apistos come from. In South America
there are few soluble carbonates exposed to buffer
the water's pH. What there is, is being leached
out & diluted by the tropical rains.  Therefore
most of tropical South America has mineral poor
water. Natural rainwater is not the same as
distilled water. You might expect it to have a
neutral pH, but the atmospheric carbon dioxide
that dissolves into the rain water forms carbonic
acid that lowers the pH of rainwater to around
5.5. Any carbonates dissolved in streams is
quickly consumed by the acid in the water.

The final pH of most South American streams
depends on the source of its water. Blackwater
streams have sources in periodically inundated
tropical rain forests not associated with
mountains or highlands. These areas have soils
that are totally leached of minerals. The plants
of these rain forests are specialized at recycling
mineral nutrients derived from organic materials
laying on the forest floor. Still, many of the
humic acids enter the water. They do this by
'steeping' the organics like steeping tea. Since
the water has almost no carbonate hardness
(alkalinity), the humic acids drop the pH below
5.5.

Clearwater streams mostly have sources in ancient
granitic highlands. These highland are the remnant
roots of mountain ranges that have been eroding
down for several hundred million years. Most
soluble minerals were leached out long ago,
leaving behind the nearly insoluble white quartz
sand that covers most of the Amazon Basin. In this
respect, their hardness is very similar to that
of  blackwater streams. The difference between the
two is that, while blackwater sources steep
organics out of the flooded rain forest debris,
whitewater streams flow in channels from the
highlands. These streams do not have the flooded
forest sources for humic acids that blackwater
streams have. Therefore their pH is closer to that
of rainwater (5.5) or slightly higher by consuming
what littler buffering alkalinity exists in the
water.

Whitewater streams have most of their sources in
geologically young mountain ranges of Peru,
Colombia, & Bolivia. They are mostly volcanic in
origin. They are a source of most of the clays &
dissolved solids in this water type. This includes
minor quantities of carbonate buffers. There is
enough to raise the pH and harden the water
moderately.

Much of the midwestern USA is covered by limestone
& dolomite. Much of the water crosses or
percolates through these carbonate areas picking
up hardness causing chemicals. Therefore these
water sources are very different from South
America. The alkalinity is so high that extreme
quantities of acid are needed to neutralize its
buffering ability before the pH will drop. When
adding acid to water you add ionic components that
may not increase the hardness, but will increase
the conductivity. Sulfuric acid will had sulfate
ions that will harden the water more that the
chloride ions in hydrochloric acid. On the other
hand, chloride ions increase the conductivity more
than sulfate ions. It has something to do with the
ionic charge. I'm not a chemist. Maybe someone
else can explain it better.

>   Oh yeah by the way ions they are particles
> which either have a positive or negative charge
> right? Also read by a meter which measure the
> time it takes to go from one probe to the next.
> Is this right?

True but all ions are not equal. See above.

>   There will be a test at the end so please pay
> attention.
>
>   It's actually scary because I understand some
> of what your saying but, I don't want to get too
> scientific with my fish they might stop spawning
> for me.<G>

I agree. The KISS (Keep It Simple, Stupid) method
is the best. Try to simulate your fish's water
without excess chemicals if possible.

Mike Wise

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