Testing water purity


drdavegoodman
 

Dear Ian and Gary;
I have looked at the Simply Hydroponics website that Gary referred me
to and it did have the answers to my question. So I'm getting one of
the TDS meters--good selection on ebay
Thanks!
Dave

--- In amelyachtowners@yahoogroups.com, amelliahona <no_reply@...> wrote:

DAVID, THERE IS NO SUCH THING AS A DUMB QUESTION!!!

Here is a site that will hopefully answer your question:

http://www.simplyhydro.com/tds-ec.htm

To quote from that site (which by the way is talking about plant
nutrient solutions, but
which are the same principles as for sea water)

"TDS, EC, PPM, microSiemens: What do all those letters mean?

What is the best way to calibrate a TDS or Ec meter?
Answer: Standard reference solutions are used. The bottles are
marked with the
conductivity (EC) value in microSiemens/cm and the corresponding ppM
values for sodium
chloride (NaCl) and potassium chloride (KCl) solutions, and
sometimes for a "442"
reference mixture. The conductivity of sodium chloride solutions is
close to that of
hydroponic mineral nutrients, so a "1000 ppM NaCl" standard is most
frequently used
when calibrating the meter for hydroponic solutions. You should
follow the calibration
instructions in the manual which the manufacturer of your meter
provided.

What does a TDS or EC meter measure?
Answer: The electrical conductivity (EC) of your nutrient results
from motion of mineral
ions when the meter applies an electrical voltage. The ppM value of
a sodium chloride
solution happens to be very close to half of its conductivity value
(in microSiemens/cm), so
many meters display the conductivity as an equivalent NaCl amount.

What does the term parts per million (ppm) mean?
Answer: It is a common unit for measuring the concentration of
elements in the nutrient
solution. One ppm is one part by weight of the mineral in one
million parts of solution.

How do I convert between TDS and EC readings?
Answer: To obtain an approximate sodium chloride TDS value, multiply
the EC reading (in
microSiemens/cm) by 1000 and divide by 2.

To get an EC value, multiply the ppm reading by 2 and divide by 1000.
Thus, if your EC is 1:
1*1000/2= 500 ppm.
And if your ppm is 500:
500*2/1000= 1 EC

Is it better to use an EC or a TDS meter?
Answer: If you have plant nutrient recommendations in EC units, an
EC meter is
convenient. If your plant nutrient recommendations are in ppM
values, a sodium chloride
TDS calibration is easier to use."

Hope this helps.

My EC meter usually shows about 500-550 microSiemens when the water
maker is
running. It will start out at 550 and fall to as low as 460 after
it has been running
for an hour or so. Water makers work better (at least the membranes
do) when
they are used for prolonged periods frequently. Thus my water maker
TDS readings
should be about 250 ppm.

Regards, Gary Silver, MD

--- In amelyachtowners@yahoogroups.com, "Dr. Goodman"
<drdavegoodman@> wrote:

Forgive my ignorance--What is a TDS reading, and how is it obtained.
Presumably it has to do with water purity?

--
David Goodman
email: drdavegoodman@
cell: 608-772-0634
STT: 340-998-2169


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