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Old 01-11-2017, 08:47 AM
GpsFrontier GpsFrontier is offline
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Join Date: Mar 2009
Location: Lake Havasu AZ.
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Hello newhydro16,
I don't recommend using a EC/TDS/PPM meter at all unless you have money burning a hole in your pocket. It's a fun toy, but simply not necessary. As for the conflicting PPM ranges. This is part of the reason relying on EC/TDS/PPM is a mistake. First of all PPM will vary from one region of the world to another, and from one manufacture to another. EC is the standard, PPM is a conversion from EC, Each manufacture uses a different conversion. Second and the biggest reason I don't even use EC/TDS/PPM meters is there are so many variables that affect nutrient uptake and optimum EC/TDS/PPM values that it's impossible to list them all. Third there are hundreds and sometimes thousands of varieties of any particular plant. There are thousands of varieties of lettuce in particular. They all have different optimum EC/TDS/PPM ranges, and that's even before considering the environmental factors that will affect the optimum range as well. Relying on EC/TDS/PPM readings and charts is a mistake. The charts are just meant to be a general guideline.

But many people begin to rely on taking a measurement and think that as long as the readings are within the recommended range, their nutrients are good, as well as balanced. But nothing could be farther from the truth. Why do people think that? Because that's what the salespeople selling them the equipment tell them. They simply don't know how to tell when a plant is healthy or not by looking at it, and easier than learning to identify the signs of over and under feeding. So they just get used to using the EC/TDS/PPM meters as a crutch. When they use the meters as a crutch it takes much longer to learn to identify problems by looking at the plant. And looking at the plant is the only real way to tell if their healthy, as well as if their being over or under fed or not.

My recommendation is to fallow the nutrient manufactures mixing instructions, and mix them to about 80% strength. (10% to 25% for seedlings, 25% to 50% when they get a little bigger, then up to 75% to 100%). Once you begin to learn how the environmental factors like temperature, humidity, and even duration and and intensity of light will affect the nutrient uptake, then you may want to adjust the nutrient strength based on the environmental factors as well. Like even weaker during hot and/or dry conditions when the plants drink more water than take up nutrients. Or a little stronger in high humidity when the plants can't drink up water as easily etc.

A general rule is 80% strength is typically just fine, especially for plants that are light feeders like lettuce. If you don't know if a plant is a heavy feeder or not, then the EC/TDS/PPM charts will help you. The plant types with the higher ranges are heavier feeders, the plant types with the lower ranges are lighter feeders. Another sign is the color of the foliage. Plants with darker green foliage are typically heaver feeders than those with a lighter green foliage. One lettuce plant may have light green foliage, and another variety may have darker green foliage. The variety with the darker green foliage would be a heavier feeder than the variety with light green foliage.
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Last edited by GpsFrontier; 01-11-2017 at 09:05 AM.
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