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Post by Apoplast on Sept 25, 2015 19:49:52 GMT -5
Hi Lloyd - Yup, those numbers didn't reveal much. You've suspected that this sand is toxic to some of your more sensitive species. It goes cloudy in vinegar. Unless you want to spend the time and money to pin down exactly what the issue is, my advice is toss it and use another type of sand. As someone who has dealt with toxic sand in the past, I can assure you that obsessing over whether it is really a problem, and if so what precisely the problem is, won't get you anywhere. Just move on.
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Post by lloyd on Sept 25, 2015 20:53:13 GMT -5
I decanted the clear supernatant vinegar (~110 cc). It's in a plastic dish. When the vinegar evaporates, I'm going to add the same amount of distilled H2O, re-dissolve the precipitate and measure the (more or less true) TDS. That will tell me if the sand I have is chemically toxic.
After reviewing the suggestions above, I am tending to the hypothesis that the medium with the (even coarse) sand just compacts too much. The peat perlite just seems to really create an aerated medium.
Anyway I'll post my results when the vinegar evaporates.
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Post by lloyd on Oct 12, 2015 20:09:53 GMT -5
The vinegar finally evaporated. I then added 0 PPM TDS water to the little dish and added the same amount of water. I then stirred the dish up, brushing the sides with my (clean) finger. TDS now 170. So either the dish was contaminated with minerals (I had cleaned and rinsed it but did I scrub the sides? Probably yes.) So it looks like the thoroughly cleaned silica sand did leach a significant amount of minerals into the vinegar.
So perhaps silica sand is not the greatest unless you really test it first.
Peat/Perlite for me now.
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Post by lloyd on Oct 30, 2015 12:47:58 GMT -5
I just realized that my idea of taking the clear vinegar/sand supernatant, letting it evaporate and adding pure water to the same volume was flawed. What I was measuring in the "TDS" of 170 PPM (really a conductivity measurement) was not a contaminant of the sand, it was almost certainly:
Silicon acetate (or Silicon tetra-acetate in solution).
So my washed sand is likely pretty clean of impurities and probably my peat-sand mix just gets compacted too much and doesn't provide enough aeration for the roots. So perlite is better for a lot of plants.
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