TDS of water after fertilzer addition.

[vpsihop@hotmail.com]

Purchased a TDS meter and some K-Lite. Was shooting for 50 ppm of nitrogen, but was shocked when I saw the meter read 500!!

Obviously forgot about all the other stuff in the fertiliser that contributes, but is there a number people try and stay under?

[terryros]

The TDS meter reading isn't close to the ppm B.

TDS meters are only approximate. What does your water source alone read?

Did you make a stock solution of K-Lite or are you trying to just add the dried fertilizer?

500 TDS is not an overly high reading if you are only going to be fertilizing once a week or so.


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[estación seca]

It depends on the plant. People suggest 50 ppm total including fertilizer for most Paphs and cloud forest plants, less for Phrags. Most other plants perhaps to 500-600.

Are you putting it in tap water?

[vpsihop@hotmail.com]

Just dried right into my watering can. RO water reading 0 ppm. It test at 130 ppm on my tap, as does another meter. I'm wondering if something is off, 1/8 TSP of K-Lite gives me a TDS of about 450 in half a gallon of water.

[terryros]

Ray always strongly suggests creating a stock solution of K-Lite from which to add to RO water. I have been a K-Lite user since it first came out.

I keep the K-Lite granules frozen until I need to make more solution. I then add 50 grams of granules to a container sitting on a scale and add RO water up to 500 grams. This is a 10% solution. I put this stock solution in a sports water bottle and keep it in the refrigerator. This makes it easy to squeeze out an accurate amount into the RO water for use. With a large collection of orchids, you would probably make a larger volume of stock solution.

30 mL of this solution into 1 gallon (3.8 L) of RO water will be 100 ppm N.

Obviously, for 50 ppm you would add 15 mL of the stock solution to the RO water.

The 100 ppm N fertilizer solution with RO water won't be over 500 TDS in my experience, but we need to remember that TDS meters vary. I have tested mine with a calibrator solution and it seems to be reasonably accurate. Calibrating it with an electrical conductivity solution, my meter is such that 1 ppm = 2 EC (I am forgetting the exact units this morning), which is a common setting for such meters.


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[Ray]

Talking to pro's in the horticulture world, it appears that orchid growers are about the only group of hobbyists that even think about TDS. Others focus more correctly on ppm N, the N-P-K ratios, and possibly ppm Ca.

Fertilizer manufacturers typically publish the mixing guide to achieve certain ppm N levels, and the EC's provided by the formula at those levels, so professionals typically control by EC.

With a granular product, especially something as coarse and heterogeneous as K-Lite, trying to use a volumetric measurement is a very rough guess, at best. As Terry said, a stock solution is the way to go, then you can let that down volumetrically with no problem.

For what it's worth 1 pound of K-Lite dissolved in enough water to make 1 gallon total, when used at one ounce per gallon, gives 125 ppm N. I prefer to store less-concentrated solutions for stability reasons, so now that I'm hand mixing again, I dissolve one pound in 2.5 gallons, and use 1 tablespoon/gallon for 25 ppm N, which I use at every watering.

Having established confidence with the concentration, you can test with your TDS meter, then use that reading as your gauge to determine how accurately you diluted the stuff. A little over or under is inconsequential.

[vpsihop@hotmail.com]

How long can I keep the stock solution pre mixed? I understand liquid fert has stabilisers in it, but would dry be the same?

[Ray]

Indefinitely, if the container is kept closed. There are no stabilizers in any fertilizer, as far as I know.

[Cheddarbob14]

Just made my first jar of solution with k-lite. Should it be refrigerated or just kept in cool/dark place? Does potting media play a role in how many tds I should be using? Does the type of orchid alter how many tds I should be using or stick to 25ppm at every watering, regardless of what kind it is?

[Orchid Whisperer]

it could be that your TDS meter is not calibrated properly. Calibrate to whatever standards were supplied with the meter.