Medpot Minstrel: Hydroponics Medical Marijuana

Thursday, January 11, 2007


Electrical Conductivity (EC) converts in funny ways

I was concentrating on parts-per-million (PPM) in my last posting. Since then, I’ve spoken to the Advanced Nutrients Medical technical help line and found out that they’ve decided to go with Electrical Conductivity (EC) values, rather than PPM.

Don’t panic. Their Nutrient Calculator still shows both numbers, so if you’ve got a PPM meter and don’t have any way of measuring EC at the moment, you can still continue using that very valuable tool to figure out the weekly diet of your cannabis plants.

Since many of us medpot growers find these different values confusing, how is this for a scoop? Even their tech guy admitted that it’s confusing! No use fretting about it—you’re not the only one who can’t figure out EC and CF and TDS and PPM, and how they all fit together.

Then the AN guy went on to relate how three different meters read EC 1. Electrical Conductivity is measured in microsiemens per centimetre.

EC 1 on a Hanna pen meter will read as 500 parts-per-million.

EC 1 on a Bluelab Truncheon meter will read as 700 parts-per-million.

EC 1 on a Utech EC meter will read as 640 parts-per-million.

Advanced Nutrients Medical has decided to go with the Bluelab Truncheon CF/EC/PPM Meter, which is manufactured in New Zealand and measures each microsiemens (mS) per centimetre as 700 PPM.

PPM and Total Dissolved Solids (TDS) are the same thing. Total dissolved solids in your nutrient solution are measured by gauging the charge between two probes—not resistance, but the conductivity of the dissolved particles.

Depending on the strain of cannabis you’re growing, the ideal EC reading might be 0.7 to 1.5 mS during the vegetative stage and 1.0 to 2.0 mS during the flowering stage. The Nutrient Calculator bears this out.

The hydroponics industry considers EC readings to be more accurate than PPM readings. CF is exactly 10 times your EC reading. So if you have a CF meter and measure 10, that reading is equivalent to EC 1.

When I was growing my medpot using Iguana Juice Grow and Bloom, plus assorted organic supplements, I was tempted to boost the size of my buds with a touch of synthetics, by adding Bud Blood, Big Bud, and Overdrive to my reservoir.

When it comes to ogranics, the Advanced Nutrients plant scientists have yet to figure out the exact amounts to use of these 3 very potent synthetic bloom boosters in terms of EC, PPM, CF, or TDS, whichever abbreviation you’re most comfortable with.

The PPM numbers in the Nutrient Calculator are merely guidelines, according to the AN tech guys. In other words, some plants like very light feedings, other plants like heavy feedings. It’s just like humans—one diet definitely does not fit all.

This is where the metering comes in. Start with a medium-feeding regimen. If you’re plants develop yellow tips, then you should decrease your concentration. If you don’t get yellow tips, it may imply that your plants are able to take a little bit more food.

Growing medical cannabis is basically experimentation. If two of your plants bolt toward your HID light, while the others are slower to grow, you should pinch the top shoots of your bolters or trim their tops entirely, to give the slow growers a chance to catch up.

If you raised your light to accommodate the fast growers, the slow growers wouldn’t have a hope. But if you pinch the top shoots of the fast ones, they’ll bush out and give the rest a fair chance.

The same way with diet. If you see any signs of calcium deficiency, include Sensi Cal Mg Mix Grow or Bloom in your nutrient regimen. If your plants show any sign of stress, feed them with Organic B or B-52.

Always be conscious when you’re adding new ingredients to the mix that your total NPK does not exceed desired levels. Keep taking pH readings and make sure that your acid-alkaline balance is at the optimum level for hydro, which is 5.6.

The temperature of your nutrient solution is also a variable and that is why some meters have an automatic temperature adjustment. The Bluelab Truncheon has automatic temperature compensation up to 78 degrees Fahrenheit.

The Truncheon is fairly reasonable in terms of price ($139.00). You’ll also need a Bluelab CF/EC cleaning kit for $24.95, since the probes have to be clean and uncontaminated for accurate readings.

For $289 you could buy a Bluelab Combo Meter, which measures pH, EC/CF/PPM, and Temperature as well. Bluelab offers calibration solutions in order to ensure that your meter is measuring your real acid-alkaline balance, and not some distortion.

Nutrients assume the form of ions when in solution. The ions in your reservoir represent the entire spectrum of minerals needed for plant growth.

My basic nutrient, for instance, is Sensi Grow A&B and Sensi Bloom A&B. In addition to the macro nutrients of Nitrogen, Phosphorus, and Potassium, this Advanced Nutrients 2-part is species-specific in including all the micro-nutrients necessary for growing robust cannabis plants.

The same goes for the classic 3-part, Grow, Micro, and Bloom, as well as Sensi One Grow and Sensi One Bloom. Each basic plant nutrient was carefully designed to meet every nutritional need of your valued cannabis plants.

So investing two or three hundred dollars in a sensitive meter to make sure that your plants are getting the proper diet in appropriate servings is not such a bad deal.

If your nutrient solution has more ions then it will read a higher EC value, since there are more ions to carry the charge from probe to probe.

EC translated into PPM using one of several conversion factors. Depending on which factor you use (the 442, the NaCl, etc.) EC 1 either means 700 PPM, 500 PPM, or 640 PPM.

It’s not unlike the confusion caused by American (or Imperial) weights and measures vs. Metric.

Be aware that Advanced Nutrients is using the 700 PPM standard, and the rest will fall into place. If you’re using a lot of their products (as I am) it would help if you bought a meter that uses the same standard.

posted by Wes @ 11:13 PM

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