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Re: TDS Meter

Hello Larry,

If your tap water reads 140 µS (or TDS) and the water hardness is 35
ppm, as measured by EDTA titration then, after dilution, for each ppm of
hardness you will read 4 µS (or TDS), PROVIDED that your dilution water
was good RO or distilled water.

If you use softened dilution water, or add add salt, pH adjusting
chemicals, or any other additives, then all bets are off. In those cases
you just can NOT easily correlate water hardness with conductivity! 

But you can use your conductivity meter in ALL cases to assess the
conductivity, which is directly related to osmotic pressure, (except for
organic additives) and thus adjust water for similar conductivity to
avoid osmotic shock while transferring fish to a different tank, or even
changing water, if you do it infrequently. You will be surprised how
much the conductivity in a tank can increase in a month!

If you have other questions, you can write me privately.

Best,

George



Larry Botkin wrote:
> 
> HI George;
>       I have a Hannah TDS meter... If I get a reading of 140  and then I
> use a titration test kit and I get a reading of 35-36 then I should factor
> my TDS readings by approx. .3 to determine a hardness of 42 when using the
> TDS meter...  Also when using salt in the water the conductivity will go up
> but the factor will  change because due to the higher conductivity of the
> salt solution...
> Am I reading you right or am I totally off base...
> 
> Larry  AKA 07805
> 
> Member - Chicago Killifish Association
> 
> At 03:28 PM 3/1/02 -0500, you wrote:
> >Hello Wolfgang,
> >
> >ALL conductivity meters measure the same thing -- conductivity. The
> >difference between the different models is
> >a) range
> >b) units in which the meter is calibrated.
> >
> >The so-called TDS meter measures conductivity and uses a conversion
> >factor for a "typical" water to express the result as Total Dissolved
> >Solids.
> >
> >Water hardness has almost no relationship to conductivity, exept that
> >hard waters have a rather high conductivity. BUT water softened by ion
> >exchange (the regular household water softener) will have high
> >conductivity and practically no hardness! A conductivity meter will give
> >you absolutely wrong "results".
> >
> >The situation is not hopeless, because the relationship between water
> >hardness of a particular water and conductivity is usually linear. So,
> >once you measure water hardness by titration (or get that value from
> >your water supplier) and then measure conductivity, you obtain that
> >"fudge factor" -- water hardness vs. conductivity.
> >
> >Because measuring conductivity is fast and simple, it is practical to
> >measure it instead of water hardness: If the conductivity of your
> >prepared water is half that of raw water, the hardness is also one half
> >of the value you measured. If conductivity is 1/10th, the hardness is
> >1/10th.
> >
> >THIS IS TRUE IF you are using either RO water or distilled water for
> >dilution. If you are using ion-exchange softened water to dilute your
> >tap water, a conductivity meter will not help you! You just have to keep
> >the dilution factor straight. (A conductivity meter is also VERY useful
> >in transferring fish to a different water/tank, so you don't give them
> >osmotic shock!)
> >
> >So, determine the range in which your tap water falls and buy that
> >meter. If you are on a municipal system, then ask the supplier about the
> >range of water hardness during the year -- it can change substantially!
> >I prefer calibration in µS/mS, because then your know WHAT you are
> >measuring!
> >
> >Best,
> >
> >George
> >
> >
> >
> >Wolfgang Schickler wrote:
> > >
> > > I am thinking about buying a TDS meter to monitor
> > > my RO unit and to take the guesswork out of
> > > preparing/mixing water for my tanks.  After looking
> > > what is available, I am somewhat confused....
> > >
> > > There seems to be different units out there
> > > measuring different things. For example here is a
> > > list of TDS tester from OAKTRON:
> > > Choose TDS 1 & 3 for testing water hardness,
> > > hydroponic fertilizer concentrations and chemical
> > > concentrations. TDS 2 & 4 are perfect for measuring
> > > low range-salinity in koi ponds, aquariums,
> > > recirculating systems and anywhere conductivity
> > > measurements are required. TDS10 measures dual range
> > > ppm/ppt. TDS20 measures dual range µS/mS.
> > >
> > > Can anybody shed some light on this? Can anybody
> > > recommend a good TDS tester that is appropriate for
> > > breeding killies? It is my understanding that
> > > hardness (Kh and GH) is most important.
> > > So the question is, do I really want a TDS tester,
> > > or is a hardness test kit good enough?
> > >
> > > Any help is greatly appreciated. Thanks.
> > > Wolfgang
> > >
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