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Re: TDS readings



> Date: Thu, 28 Dec 2000 04:56:14 -0800
> From: Steve Pushak
>
> Since I suspect that its the osmotic pressure due to various
> salts in the water that are most important, the TDS meter
> might be even more useful than a "hardness" indication
> when dealing with water which has mainly just the primary
> salts in it: (K, Na, Mg, Ca, NO3, Cl, CO3, SO4, H & OH)...

My thoughts exactly.

> I wonder if anybody has really tried to investigate the
> importance of humins for breeding Tetras and Discus.
> Does anybody know?

Peat- derived humics were apparently pretty critical to the intial German
success in breeding Discus back in the '60s. I believe you might be able to
find references in European literature.

Perhaps if Ole Larsen still follows the list he might be able to provide you
with some. I've discussed it in passing with him off and on for a couple of
years, but I've never knuckled down to pin the specifics...


> Date: Thu, 28 Dec 2000 09:36:00 -0700 (MST)
> From: Roger S. Miller

> When did "Maybe" become an obvious disagreement?
> Conductivity meters have a number of uses.  "Maybe"
> other people will find the meter to be "most" useful for
> something else.

Silence can normally be read as consent, while most people consider an
interjection as the beginning to "something else".

The options from there are rather limited - agree, disagree, clarify, or ask
for clarification. I didn't see a question mark for punctuation, nor any
additional comments which could possibly be interpreted as clarification.

Ambiguity does arise with the use of such an indefinite as the sole
response. Don't forget - I did follow with:

"Perhaps you could share a few thoughts here - at least give us an idea as
to where you're headed?"

Which you "obviously" have, now ;-)

> First, the original question was over the use of TDS values
> from a TDS meter...

I'm sure glad about that - especially since I provided one. Although,
reading further...

> The method you describe here is based on conductivity
> values.  I don't know that K9AUB's meter even gives
> conductivity readings.

and slightly later...

> I've used conductivity measurements (generally laboratory
> measurements) to estimate a lot of things over the years
> and in many instances I've had the opportunity to check
> the estimates against actual analyses.  Estimates
> based on conductivity are *not* generally accurate.

If you've indeed been using them for so long, then you probably know the
difference between a gravimetric test and a conductivity measurement. No
problem there. But then, as you say, you don't know what type of meter the
poster obviously has. Perhaps the confusion lies in separate assumptions
we've _both_ made.

You appear to me to assume the meter in discussion to be a true gravimetric
TDS. (I could be wrong - that's why they call it an assumption.)

I assume the meter is actually a conductivity meter that is merely labeled
as TDS, which is by far its most commonly- available "guise" in _this_
trade.

> Second, a conductivity meter measures conductivity,
> not hardness.  The method you describe below allows you
> to *estimate* hardness from a conductivity reading and
> other data about the water sample from other sources.  That
> is not a measurement of hardness and it isn't (in an
> analytical chemistry sense) a determination of hardness.

Which is _exactly_ the reason I explained things like knowing the
composition (and the futility of working with an unknown sample) and the
proper conversion factors.

And again I say "starting with water of _known_ purity, and adding chemicals
of _known_ compositions in no way restricts the use of the meter for such
determinations."

Chemists are the same as engineers, architects, physicists and burger
flippers. They all use little "tricks" to give them "estimates" and "ball
park figures". Even the Army has a term for it - "field expedience". Just an
intelligent substitution and modification of what's "on hand" for what's not
and needed...

> Public water utilities in the US are required to provide their
> users with some information about their water quality.  I
> don't think the conversion between TDS and conductivity is
> among those things.  In fact (with some state to state
> variation) I don't think that either TDS or conductivity are
> commonly regulated under health standards, so the utility
> may not have to provide either of those.

I'm sorry - did I slip up and type the word "requirement" somewhere? 'Cause
I sure can't find it!

It's a number that they _normally_ come up with in the course of their own
work. It is often, as a _courtesy_, listed in the quality reports (as is the
case with Tennessee- American, my own source). And as a _courtesy_, any
information that's *not* listed directly on the report can normally be had
for the price of a phone call. I've even dropped them an e-mail for a couple
of parameters that aren't listed anymore, and they sent me a copy of their
entire analytical spreadsheet for that quarter.

Now, perhaps you could do me the _courtesy_ of not adding words to my
postings? It'd save you quite a bit of typing...

> > So, when I set up something like a breeding tank for D. filamentosus,
then
> > I'm shooting for mid-4 pH values and _total_ hardness values of less
than 1
> > dGH. None of my hobby kits can give me this sort of resolution. A pH
meter
> > gives me the acidity values, and a conductivity meter gages my "dilution
> > ratios". Starting with a premix of 3:1 Ca:Mg salts, I can dilute to
conducti
> > vity readings in the 10-15 5S range. Using a conductivity conversion
factor
> > of ~0.74 (the range of values is ~0.6 - 0.9, dependent on composition)
for
> > the types of salts I'm using tells me that the water is about 7-12 ppm
> > hardness. Add to peat and I'm in business.
>
> Do you grow plants in that water?

Indeed I do. Heavy on the root feeders and Java Moss. Almost anything that
has roots in the substrate and grows emergent.

Stemmed "bunch" plants have the most interesting growth patterns in those
conditions. Things like Red Ambulia (Limnophila sessiliflora) actually grow
like little "miniature" versions of themselves. Not like bonsai, where the
growth is merely stunted, but like a miniature Collie compared to a full-
sized one. Surprisingly healthy, too - the stems are pretty stiff and tough
as all get- out -- tougher to break than "normally" raised ones. Just wish I
could get the red in them *as* those miniatures, but the water's too sterile
for that.

I did forget to mention that it's actually a combination of peat and CO2
that I use to achieve the low pH values. As far as the water goes, that's
probably the only nutrient that _is_ freely available (save for any
ammoniums through fry or food decomp, but the aim is to keep *them* low, so
they're not _much_ of a factor).

And as I use a lot of root work (and as I just mentioned in response to
Tom's post on soft water), it seems especially prone to Cyano at times
around the wood.

But as you would suspect - and are apparently trying to point out - it's not
the most successful venture going. I believe the gist of that passage dealt
with fish breeding, though I can appreciate your curiosity. Rarely do I keep
a tank at those values _permanently_. Once the breeding and initial fry
rearing are accomplished, the tank is usually allowed to creep up to values
more traditionally described as "Amazonian" - low- to mid-6 pH and a couple-
three degrees of "hardness" (sorry, Steve).

> You're asking for quite a bit of accuracy out of your meter.  I
> use a rather expensive professional-quality conductivity meter
> in field work. It's kept clean and its calibration is checked
> regularly.  Despite that I don't expect it to produce results as
> accurate in the very low range as you want out of yours.

"Maybe" I've been mislead about the electronics, then. Since I calibrate the
thing to 40 ÁS samples, I'd have thought it to be more accurate at half
resolutions than ones with a few extra zeroes added in.

But you may be thinking of things like probe sensitivity, at which point I
must defer to experience on your part. Umm...and I believe there might be a
lot of other Apisto and Killie breeders who might need to know if this is a
significant factor. Your chance to really shine here, since we tend to keep
to the very low side of things...

> I've used conductivity measurements (generally laboratory
> measurements) to estimate a lot of things over the years
> and in many instances I've had the opportunity to check the
> estimates against actual analyses.  Estimates based on
> conductivity are *not* generally accurate.

Estimates.

Accuracy.

Hmm...I believe they convey different concepts, do they not? As well as
providing differing degrees of utility?

Gosh, come to think of it - did all that 'splainin' I did on emperical
comparisons go to waste?

> I think hobbyists who need to know about their hardness
> will be much better off with reagent test kits.  An inexpensive
> Tetra kit will tell you whether the water is in the range of 0-9
> ppm or 9-18 ppm (0.5 degree increments).  If you use your
> own glassware you probably can get it to read down to 0-4.5
> ppm , 4.5-9, 9-13.5 and 13.5-18 ppm (quarter degree
> increments).

You know that. I know that. In all likelihood, most of this list knows that.
As well as adjuncts such as drop and sample size consistency, knowing to
dilute the sample in the first place, etc., etc..

But we're such a _large_ percentage of the hobby, aren't we?

> Conductivity meters are quite commonly used for monitoring
> gross changes in water quality and I agree that this is a good
> use...

Why, thank you!

> Still, you need to make sure the meter is well calibrated or
> what looks like a change in your water quality may just be
> a change in the meter calibration.  Or the temperature. Or
> something else...

Sound advice for any instrument of measure.

At least we can end on a couple of good points...

-Y-