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 Total Dissolved Solids

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JohnnyAMH
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PostSubject: Total Dissolved Solids   Mon May 12, 2014 4:44 pm

I recently received a Total Dissolved Solids (TDS) Meter. I noticed that there has been little discussion about the importance or unimportance of TDS in this forum. I have found a few links to share. All comments are welcome… study 

Here’s a link to some basic information…
Total Dissolved Solids Basics

Here’s a link to some detailed but possibly debatable information…
Total Dissolved Solids Detailed

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30 gal. Bare Bottom Adult Angelfish Tank
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gerald
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PostSubject: Re: Total Dissolved Solids   Mon May 12, 2014 7:07 pm

A "TDS meter" is really a conductivity meter. It's measuring only the dissolved solids that contribute to electrical conductivity (mainly salts and metal ions). It's NOT measuring the dissolved organic carbon molecules (tannins, lignins, "blackwater" chemicals) that dont affect conductivity. The readout on a "TDS meter" is therefore based on an assumed ratio of TDS to conductivity, which is about 0.50 if the predominant ions are sodium and chloride, or about 0.65 for a typical mix of ions found in most freshwater lakes and rivers. Raleigh tap water (from the Neuse River) has an average TDS of 165 mg/L and average conductivity of around 250 microSiemens. TDS:Cond ratio = 0.66. Richmond water is probably pretty similar.

In blackwater rivers with lots of organics but few ions, conductivity is still a useful measurement but it's NOT a good way to measure TDS. To actually measure TDS in blackwater you need to filter a water sample, evaporate the water, then weigh the dry residue. The TDS will be much higher than what your "meter" shows because the meter isn't detecting all that the non-conductive organic (brown) stuff. For aquarium-keeping purposes, conductivity is usually good enough.

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JohnnyAMH
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PostSubject: Re: Total Dissolved Solids   Mon May 12, 2014 9:06 pm

@gerald wrote:
A "TDS meter" is really a conductivity meter.  It's measuring only the dissolved solids that contribute to electrical conductivity (mainly salts and metal ions).  It's NOT measuring the dissolved organic carbon molecules (tannins, lignins, "blackwater" chemicals) that dont affect conductivity.  The readout on a "TDS meter" is therefore based on an assumed ratio of TDS to conductivity, which is about 0.50 if the predominant ions are sodium and chloride, or about 0.65 for a typical mix of ions found in most freshwater lakes and rivers.  Raleigh tap water (from the Neuse River) has an average TDS of 165 mg/L and average conductivity of around 250 microSiemens.  TDS:Cond ratio = 0.66.  Richmond water is probably pretty similar.

In blackwater rivers with lots of organics but few ions, conductivity is still a useful measurement but it's NOT a good way to measure TDS.  To actually measure TDS in blackwater you need to filter a water sample, evaporate the water, then weigh the dry residue.  The TDS will be much higher than what your "meter" shows because the meter isn't detecting all that the non-conductive organic (brown) stuff.  For aquarium-keeping purposes, conductivity is usually good enough.

Thanks for your comments. The little research that I have done so far supports your statements. I'm not trying to replicate a South American  Blackwater environment but I do hope get a better understanding of what's going on with my tanks waters... Cool

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     ~~~ My Aquariums ~~~
55 gal. Planted Community Show Tank
(Swordtails, Neons, Kuhlii Loaches and Bristled Nose Plecos)
30 gal. Bare Bottom Adult Angelfish Tank
20 gal. Bare Bottom Angelfish Breeder Tank
10 gal. Bare Bottom  Angelfish Fry Tank
10 gal. Planted Show Tank
(Guppies and Bristled Nose Plecos)
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