“Total Dissolved Solids” - TDS

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Orchid Iconoclast
Staff member
Jun 9, 2006
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Oak Island NC
I suspect in person lectures will largely be superseded in the future. Which talk are you giving at Marin? They meet the same night as Mt. Baker and we often "share" on Zoom. I don't know if our new VP will continue that practice, but it has worked well in the past. We had planned to meet in person in January, but given the statistics for this area that I saw today, I'd say unlikely.
The Marin talk will be about the use of microbial products and phytochemical stimulants in orchid growing.

I just got out my TDS meter and inspected it more closely. It has a Mode button that can be switched between TDS, uS/cm, which I believe means microSiemens/centimeter (which means nothing to me) and temp in C and F (not sure why).

So I took 1/4 tsp of K Lite and put it in a gallon of RO water, and it came out 253 ppm (about what I expected) and 538 uS/cm. So, Ray, what do I make of that? (I don't have Greek letters easily available, but I'm sure you understand.)
I recommend getting a bottle of standardized EC solution and calibrating.

If mixed with pure water (EC=0. Don’t forget that the EC of the water has to be deducted from the total to determine the fertilizer contribution) an EC of 538 suggests the solution is about 70-75 ppm N. I would guess that a quarter of a teaspoon should give about 50 ppm N, which would have an EC of about 350 uS/cm and a true TDS of about 375 or thereabouts.

(I prefer using my PC keyboard over the iPad, and the ASCII symbols come in handy - left Alt key + 0176 gives the degree symbol and 230 gives a mu.)


Well-Known Member
Nov 20, 2013
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I think I still have a Marin link, or perhaps we're meeting with them jointly still. LOL. If not, I'd be ditching my own meeting, as I'd like to hear your talk. You give some of the best talks out there.

Thanks for your reply. But are you really giving up your talks on S/H? That would be a shame.

I suspect in SH what I'm doing now is probably close enough, and I'll probably leave it as is without obsessing about it. The plants seem happy.

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