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Thanks for your thoughts on this, Mark. I quite agree that my
original query will likely not be fully answered, and I really wasn't trying to
create this much discussion!
I have to challenge a couple of your comments, though, as much for my own
education as anything:
> (This one is probably
semantic) Seems to me that an EC meter is measuring the conductivity of a
solution, not of the components of it, per se. Maybe true salts affect the
conductivity more than other minerals, but they are all involved in the solution
conductivity to some degree. Magnesium carbonate is not a "salt" but does
affect conductivity.
> "Ingredients like urea do not
conduct at all" ??? It hydrolyzes upon contact with water, and decomposes
(with time and temperature) to release ammonia and carbon dioxide into
solution. Also, if it does not conduct at all, that would suggest that no
matter how much you put into solution, a TDS meter would never indicate its
presence. Is that right? (Doesn't seem so to me, but I'm only
guessing...)
Ray Barkalow - First Rays Orchids - www.firstrays.com Plants, Supplies, Books, Artwork, and Lots of Free Info! . ----- Original Message -----
From: [EMAIL PROTECTED]
Sent: Tuesday, January 18, 2005 2:21 AM
Subject: [OGD] Re: EC & TDS Ray, I don't think you will ever nail down a factual background as to why we focus on TDS as oppose to EC. My thoughts: I do think most orchid growers don't use a TDS/EC meter and don't have too. Most growers rely on fellow local growers, books, and if they really dig, their local water department for their information on water quality. Then they add fertilizer by following the directions on "orchid specific" fertilizers or a 1/4 to a 1/2 teaspoon of regular fertilizers to their chosen water source. Orchid growers are very attuned to the amount of salt in their water and fertilizer. As beginning orchid growers you hear about salt in tap water, fertilizer, and flushing out salts in pots because orchids are more to very salt sensitive compared to other house or hobby plants. I think it is easier to explain to a learning grower, and for growers to think in TDS (ppm or ppb) then EC (mMho). My local water quality report comes in ppm and ppb. I would not be surprised if many orchid growers confuse TDS, Total Dissolved Solutes, and think TDS means "total dissolved salts". A TDS/EC meter measures electrical conductivity of pretty much only salts and is only relational approximation of TDS. Different fertilizer salts conduct electricity different, and ingredients like urea do not conduct electricity at all. Throw in concern about solution temperatures, talk about TDS/EC meters can get complicated and confusing. Cutting this short, it is getting late, I think most orchid growers just want to know about how much salt they are applying to their orchids- the "total dissolved salts" in a solution. Mark Sullivan _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com |
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