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PPM
Sept 24, 2014 11:44:30 GMT -5
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Post by Maiden on Sept 24, 2014 11:44:30 GMT -5
Maybe some of you guys can light my lantern...
Each month i buy a 20L of water from a local water store. Before using the water i always test it with my tds meter. Its always 0ppm, and i water my cps with it.
Once a month a use a turkey pump to suck the excess water in the bottom of each terrarium. And i use that water to water my non-cp plants. Just for fun i tried to test that used water with the tds meter. I was very surprised with the result. 198ppm! Its kinda rock hard water!
Its probably a very basic thing that i dont understand, but how a 0ppm water can be at almost 200ppm after running in a single peat/perlite mix pot? Where all these mineral salts came from?
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PPM
Sept 24, 2014 11:52:14 GMT -5
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Post by hal on Sept 24, 2014 11:52:14 GMT -5
It's not necessarily mineral salts, just organics dissolved in the water.
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PPM
Sept 24, 2014 11:59:23 GMT -5
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Post by Maiden on Sept 24, 2014 11:59:23 GMT -5
Mmh ok. I was sure this lil tester was only for minerals ...
I feel kinda stupid.. ;-)
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PPM
Sept 24, 2014 12:10:09 GMT -5
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Post by hal on Sept 24, 2014 12:10:09 GMT -5
They measure conductivity of the water so any ions in the water will affect the reading. They assume you are testing clean or treated water so if you test dirty water they aren't too accurate.
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PPM
Sept 24, 2014 12:23:03 GMT -5
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hal likes this
Post by Maiden on Sept 24, 2014 12:23:03 GMT -5
I learned something today, thanks ian
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Post by lloyd on Sept 24, 2014 18:36:22 GMT -5
To get an idea of what Ian is saying-take various substrates, e.g.: peat, LFS, silica sand; add distilled water (TDS 0) and measure the TDS of the drain water from each. Pure silica sand will give a TDS of around 11 or so PPM. Peat water will be around 40-50 or so. LFS in between. As the peat breaks down, the TDS will go up (higher organic acids, etc.). These will not bother CP's.
What will kill CP's are are the carbonates, magnesium compounds and other minerals that are in Toronto tap water for instance.
On the other hand testing effluent can be useful. I use to use this broken clay stuff in the bottom of my micro-bogs for drainage. I always assumed it was just clay. One day I measured the TDS of the drainage water and it was scarily high. I figured it must be the aggregate (Peat/perlite otherwise). Sure enough I tested drain water from fresh aggregate and it was way too high! Repotted my microbogs with inert sumidero balls and mineral fibre cubes.
So when you measure TDS with one of the cheap meters we use, as Ian says you are not really measuring TDS but conductance which is related to TDS if the sample isn't contaminated with organic material.
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Post by cory on Sept 24, 2014 19:38:22 GMT -5
Good question maiden!
Great replies I learned something new today myself
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