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RE: dH/TDS

Well, I didn't reply to the first post because I thought Wright would 
surely do so  .... :o)

The answer below is not quite right, so here goes .......

>Since no one replied I will take a shot.
>
>On 08-Sep-00 Ryan Deal wrote:
>>  Hello,
>>      I was wondering if there is any "link" between dH and TDS.
>>
>
>Not much.


This much is true. Conductivity, which is measured by TDS meters, is 
a function of the total dissolved salts, including those that do not 
have anything to do with hardness. If you add salt to your water it 
will have a high conductivity and hence a high TDS. Sea water or 
brackish water will also have high TDS. Water that comes from your 
tap, however, that has a high TDS is very likely to be hard, as the 
most likely salts producing the conductivity are those that 
contribute to hardness. Water that has a very low TDS will certainly 
be soft.

Hardness is a measure of Ca and Mg in the water (with a very minor 
contribution by certain others that can be ignored). So-called 
temporary hardness (also referred to as carbonate hardness, a 
misleading term) is due to bicarbonates of Ca and Mg, which are 
reasonably soluble. When the water is boiled carbon dioxide is driven 
off and Ca carbonate is precipitated (if sufficient is present). This 
is what causes the deposits of scale to form in your kettle if you 
have such water. Permanent hardness is due to other Ca and Mg salts 
and cannot be removed by boiling. Hard water is difficult to wash 
with if you were to use true soaps because Ca soaps (ie. calcium 
salts of fatty acids) are insoluble.

By the way Ca=calcium, Mg=magnesium.

The bottom line is that a high TDS will often be a rough indicator of 
high hardness. Very low TDS indicates soft water.

Barry Cooper

>
>dH or GH is total hardness. It is measure of combined carbonates, sufides,
>sulfates, silicates, etc.
>
>TDS is a measure of ion conductivity.
>
>Now the ions that will contribute to GH will also contribute to TDS, but the
>recipricol is not the case.  Things like NaCl or KCl will contribute 
>greatly to
>the TDS but very little if any to the GH.  So your question:
>
>>For instance,
>>  if the water had a dH range of 7.0-9.0, what would that be equal to in TDS
>>  terms (if they are related at all?).
>>
>
>can not really have an accurate answer.  If the mono ion concentration is
>constant then the TDS might be an indicator of GH but you would need to
>calibrate it for your water. In fact, I really do not know why people use TDS
>with Killies.  It is used a lot with Discus and this is becuase at 
>the dH (0 -1)
>that people use to raise Discus, if the TDS is low the slime coat on 
>the Discus
>is inhibited.  This makes successful fry rearing very hard.
>
>I know of no corresponding situation with Killies.  I use the American
>Pharmaceuticals GH and KH test kits and use no measure of TDS.
>
>>  I just ordered my R.O. unit and I was
>>  wondering how to measure the dH?
>>
>
>I use the American Pharmaceuticals GH and KH test kits and use no measure of
>TDS.
>
>>  I am buying a pH and TDS meter and I am
>>  wondering if I can use the TDS meter to get an idea of what the dH is? Do I
>>  need to get another meter for the dH? I notice that in most books they give
>>  you the dH that the fish prefers, but nothing about the TDS.
>>
>
>Thus the logic of measuring GH and not TDS.
>
>>      Also what is the best way to change the dH of my R.O. water? When I
>>  change the dH of the water am I adding buffers?
>>
>Aquarium Phamiceuticals and Kent both make a product to adjust dH from R.O.
>water.  I think they are both called R/O Right.  Aqua Pham's is a 
>liquid and is
>much easier to use.
>
>Note that you often have to do a small pH adjustment too.  Do this 
>after you do
>the R.O. adjustment.  Don't waste money on the pH adjustment 
>chemicals.  a 10:1
>ration of Baking Soda/Soda Ash (available at swinging pool supply stores). It
>will be the same thing for about 1/100th the cost
>
>>      If there is anyone out there that would like to give a dissertation on
>>  dH, TDS, pH, kH, etc. and how they work together and how they can be changed
>  > and measured to get the optimal parameters from the R.O. water, it would be
>>  GREATLY appreciated.
>>      Thanks in advance for any replies.
>>
>>  Thanks,
>>  Ryan
>>  ryand at mtxaudio_com
>>
>>
>>  ---------------
>>  See http://www.aka.org/AKA/subkillietalk.html to unsubscribe
>
>----------------------------------
>E-Mail: listhub at libros_andante.mn.org
>Date: 11-Sep-00
>Time: 12:01:18
>
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Barry J. Cooper				Phone: (607)253-3336
Dept. Biomedical Sciences			email: bjc3 at cornell_edu
College of Veterinary Medicine
Cornell University, Ithaca, NY 14853
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