Re: [Killietalk] TDS vs Conductivity

[Barry Cooper <bjc3 at centurytel_net>]

To make sure everyone is on the same page here, some substances 
dissolved in water would have colligative properties and affect such 
things as osmotic pressure without being measured by a conductivity 
(i.e. TDS) meter, which is what I think Lee is getting at. A good 
example would be sugar. There are likely to be some such substances in 
aquarium water (not sugar, but other non-ionized organic substances) but 
their contributions to osmotic pressure, etc. would usually be 
negligible compared to ions.

Barry

Barry J. Cooper
Sweet Home, OR 97386



LeeH920226 at aol_com wrote:

>In a message dated 2/2/06 1:27:06 PM, bjc3 at centurytel_net writes:
>
><< Am I not correct in saying that the conductivity, which is what all 
>these meters read, is dependent on the number of charged species in the 
>water, mostly simple ions like Na+, Ca2+, Mg2+, Cl-, carbonate, 
>bicarbonate, etc >>
>
>Exactly right. TDS does not mean what it says. What is important are those 
>colligative materials that affect the osmotic pressure. Conductivity is a very 
>simplified way  of measuring it, although very useful. Expressing it as TDS is 
>useful, if misleading. Probably should be called apparent ionic dissolve 
>solids. However that creates an acronym, already in use.
>
>Lee Harper
>Media, PA
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