about TDS

Thusly "NetMax" Spake Unto All:

TDS is a (roundabout and ambiguous) measure of the electrical
conductivity of a water, which in turn is a measure of the salinity of
the water.

I think your intro is reversed, it should read:
"Measuring the electrical conductivity of water is a roundabout method of
determining the level of TDS."

I don't really see that. I mean, yeah, it's good to know the
conductivity of the water, and yeah, the conductivity is dependent on
the amount of dissolved salts.
I just question the use of measuring conductivity but expressing it as
fictional milligrams of the wrong salt per liter. I really don't see
the point.

IMO, measuring the conductivity is useful only to judge the purity of the
water. While it does indirectly indicate TDS and/or salinity to some
degree, there are better ways to measure those. A conductivity meter on the
output of a RO/DI system is a great way to see if the output is pure, and it
needs no calibration or cleaning.


"Mean_Chlorine" wrote in message
...
Thusly "NetMax" Spake Unto All:

TDS is a (roundabout and ambiguous) measure of the electrical
conductivity of a water, which in turn is a measure of the salinity of
the water.

I think your intro is reversed, it should read:
"Measuring the electrical conductivity of water is a roundabout method of
determining the level of TDS."

I don't really see that. I mean, yeah, it's good to know the
conductivity of the water, and yeah, the conductivity is dependent on
the amount of dissolved salts.
I just question the use of measuring conductivity but expressing it as
fictional milligrams of the wrong salt per liter. I really don't see
the point.

Thusly "Glenn" Spake Unto All:

IMO, measuring the conductivity is useful only to judge the purity of the
water. While it does indirectly indicate TDS and/or salinity to some
degree, there are better ways to measure those.

Actually, no, there aren't. There are other ways of measuring
salinity, ie relative density or refractive index, but not more
accurate, which is why salinity is defined as the electrical
conductivity ratio of a standard potassium chloride solution
(http://www.corrosion-doctors.org/Sea...definition.htm)

For TDS there's no other way period.

A conductivity meter on the
output of a RO/DI system is a great way to see if the output is pure, and it
needs no calibration or cleaning.

The reading you get on a RO/DI is usually the electrical resistivity,
not the electrical conductivity. They're pretty much the same thing,
but resistivity is the inverse of conductivity, ie as one grows the
other decreases.

I guess one could put it as that conductivity is a measure of _how
much_ salt there is in the water, whereas resistivity is a measure of
_how little_ salt there is in the water.

(If you're ever unsure, look at the units. Electrical resistance is
measured in Ohm, electrical conductance in Siemens. Resistivity and
conductivity are derived from these, and have Ohm*meter and
Siemens/meter as base units.)

"Mean_Chlorine" wrote in message
...
Thusly "NetMax" Spake Unto All:

TDS is a (roundabout and ambiguous) measure of the electrical
conductivity of a water, which in turn is a measure of the salinity
of
the water.

I think your intro is reversed, it should read:
"Measuring the electrical conductivity of water is a roundabout method
of
determining the level of TDS."

I don't really see that. I mean, yeah, it's good to know the
conductivity of the water, and yeah, the conductivity is dependent on
the amount of dissolved salts.
I just question the use of measuring conductivity but expressing it as
fictional milligrams of the wrong salt per liter. I really don't see
the point.


I'm not questioning the wisdom of using conductivity to estimate the
level of TDS. I also agree that the accuracy will depend on the
percentage of conductive materials which make up your TDS. It's just
that the measurement method (conductivity) is not the measurement (TDS).

TDS is a parameter, which can be measured in different ways.

Conductivity is a characteristic. It's typically used to determine a
material's resistance (by taking the inverse of the mhos to give you ohms
of resistance). This is useful to determine if the material is more
insulator or conductor, and its suitability for various applications
(typically electrical, as it's the movement of electrons which are
influenced by a material's resistance or conductance). As a measurement
method, it just so happens to give a pretty good approximation of the TDS
level.

So conductivity (how you measure) is an indicator of the TDS level (what
you are measuring), not the reverse (at least not in any applicable sense
;~).

Oversimplified: temperature is not a method of measuring a thermometer -
a thermometer is a method to measure temperature.

I'm sorry if I'm not making myself clear enough, perhaps I'm nitpicking
anyways.
--
www.NetMax.tk

Thusly "NetMax" Spake Unto All:

I'm not questioning the wisdom of using conductivity to estimate the
level of TDS. I also agree that the accuracy will depend on the
percentage of conductive materials which make up your TDS. It's just
that the measurement method (conductivity) is not the measurement (TDS).

If I'm reading you correctly, you're saying that you're interested in
finding out the number of milligrams of salt there are per liter, not
in finding out how good the water is at conducting electricity.

This is true. However, while we're picking nits, I'd say that what
you're really interested in, is the osmotic potential of the water
relative the cells of the organisms in your aquarium, which you
estimate by estimating the salinity through measuring conductivity,
while assuming that non-ionic compounds do not make a significant
contribution to osmotic potential.

;-)

So conductivity (how you measure) is an indicator of the TDS level (what
you are measuring), not the reverse (at least not in any applicable sense
;~).

Oversimplified: temperature is not a method of measuring a thermometer -
a thermometer is a method to measure temperature.

It would be better put as that when you use an alcohol thermometer,
what you measure is temperature-induced volume change, whereas what
you estimate is temperature.

What you measure with a conductiometer or with a TDS-meter is
conductivity. The difference between them is that a TDS meter makes an
added assumption about which salt is responsible for the conductivity,
and estimate salinity.

MY point is that to the aquarist it doesn't really matter if the
reading is in uS/cm or mg/L salt, but the aquarist will find it easier
to find information about the conditions in the home waters of his
fish expressed as uS/cm than in mg/L salt, and the conversion to mg/L
makes the reading less accurate/more ambiguous.

I'm saying that I don't see the point with converting from uS/cm to
ppm salt. I see the point with converting volume expansion to degrees
for alcohol thermometers, but I don't see the point with ppm salt.

I mean, you're interested in finding out if the water is suitable for
your fishes, and the measurements you can find from, say, Rio Negro,
or Tanganyika, will be in uS/cm (or mS/m), not in ppm salt. Am I
right?

So what's the *point* of converting to ppm salt?

"Mean_Chlorine" wrote in message
...
Thusly "NetMax" Spake Unto All:

I'm not questioning the wisdom of using conductivity to estimate the
level of TDS. I also agree that the accuracy will depend on the
percentage of conductive materials which make up your TDS. It's just
that the measurement method (conductivity) is not the measurement
(TDS).

If I'm reading you correctly, you're saying that you're interested in
finding out the number of milligrams of salt there are per liter, not
in finding out how good the water is at conducting electricity.

This is true. However, while we're picking nits, I'd say that what
you're really interested in, is the osmotic potential of the water
relative the cells of the organisms in your aquarium, which you
estimate by estimating the salinity through measuring conductivity,
while assuming that non-ionic compounds do not make a significant
contribution to osmotic potential.

;-)

LOL, agreed, or at least what level, difference and at what rate of
change does osmotic pressure cause stress to the particular fish species
under consideration. We might find that the better measurement method in
the future does not even count electrons to do the extrapolation.

So conductivity (how you measure) is an indicator of the TDS level
(what
you are measuring), not the reverse (at least not in any applicable
sense
;~).

Oversimplified: temperature is not a method of measuring a
thermometer -
a thermometer is a method to measure temperature.

It would be better put as that when you use an alcohol thermometer,
what you measure is temperature-induced volume change, whereas what
you estimate is temperature.

What you measure with a conductiometer or with a TDS-meter is
conductivity. The difference between them is that a TDS meter makes an
added assumption about which salt is responsible for the conductivity,
and estimate salinity.

MY point is that to the aquarist it doesn't really matter if the
reading is in uS/cm or mg/L salt, but the aquarist will find it easier
to find information about the conditions in the home waters of his
fish expressed as uS/cm than in mg/L salt, and the conversion to mg/L
makes the reading less accurate/more ambiguous.

I'm saying that I don't see the point with converting from uS/cm to
ppm salt. I see the point with converting volume expansion to degrees
for alcohol thermometers, but I don't see the point with ppm salt.

I mean, you're interested in finding out if the water is suitable for
your fishes, and the measurements you can find from, say, Rio Negro,
or Tanganyika, will be in uS/cm (or mS/m), not in ppm salt. Am I
right?

So what's the *point* of converting to ppm salt?

This isn't a field where I can claim any proficiency, but I think that
they are using the salt ppm level to express a 'stress' level rather than
an absolute level of conductive salts (which may or may not accurately
represent the elements causing osmotic pressure, and may or may not
represent the distribution of salts existing in the specie's point of
origin). Leaving it in Siemens or mhos is a bit more 'honest' if you
like. To understand what the conductivity number represents, you require
a more detailed description, which should include its limitations
relevant to our application - so yes, I agree.
--
www.NetMax.tk