Quote:
Originally Posted by loveisallyouneed Great post babygro. I forget who posted it but it was a great link to calculate ppm as far as nutrients go and ever since then i've been working in ppm but have always wanted to know about EC. What is normal/safe ppm for nutrients during the different stages of growth? Thanks |
Hiya loveisallyouneed
Glad you enjoyed the post, and thanks for the link, unfortunately it won't work on my antiquated computer! Probably java driven - my machine burps when it hits java. The safest level for feeding at any stage as far as I'm concerned is as I said, about 0.8-1.0 EC maximum, ideally more 0.6-8.0 for small regular feedings. That applies at any stage of growth apart from seedlings and clones for the first 2 or 3 weeks.
I'm not sure what ppm scale you're working to, so here's a conversion guide -
EC = Hanna, Eutech, Truncheon
0.1 EC = 50ppm, 64ppm 70ppm
0.2 EC = 100ppm, 128ppm 140ppm
0.3 EC = 150ppm, 192ppm 210ppm
0.4 EC = 200ppm, 256ppm 280ppm
0.5 EC = 250ppm, 320ppm 350ppm
0.6 EC = 300ppm, 384ppm 420ppm
0.7 EC = 350ppm, 448ppm 490ppm
0.8 EC = 400ppm, 512ppm 560ppm
0.9 EC = 450ppm, 576ppm 630ppm
1.0 EC = 500ppm, 640ppm 700ppm
So, if you're using the Hanna scale, somewhere between 300ppm (0.6 EC) and 500ppm (1.0), ideally 400ppm (0.8EC).
The following is cut and pasted from the old Overgrow FAQ guides, so I take no credit for the information contained - that comes from elsewhere. It's a really useful guide to converting NPK ratios into ppm, although don't ask me what scale they're using! It should give people a reasonable idea of what levels to feed at based on the NPK ratio of the fertiliser they're using which can really help if you don't have an EC meter.
Converting Fertilizer NPK Ratings to PPM and Teaspoons per Gallon
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One can estimate the parts per million in solution (ppm) produced by a quantity of fertilizer in a gallon of water, based on the fertilizer's N-P-K rating.
For each number in the rating apply the following formula:
> one teaspoon (5ml) of a given fertilizer in a gallon of water
(10xN)÷ 0.768 = ppm
> one tablespoon (15ml) of fertilizer in a gallon of water:
(10xN)÷ 0.256 = ppm
Example: Peter's Professional All-Purpose Fertilizer with N-P-K rating of 20-20-20.
(10x20)÷.768=260.4 ppm
Therefore, one teaspoon (5ml) of Peter's Professional All-Purpose 20-20-20 in one gallon of water will produce a solution that contains approximately 260.4 ppm of Nitrogen, 260.4 ppm of P (P2O5), and 260.4 ppm of K (K2O) for a TOTAL ppm of approximately 781.3 .
Explanation
It's important to understand that with the term "parts per million," we are expressing a measurement in terms of a RATIO, which, like miles per hour or pounds per square inch, is a relation in degree or number between two separate measurements. "Parts per million" is a common way of expressing the measurement of the dilution of something in solution, which for our purposes here, is the dilution of fertilizer components in water. It just so happens that fertilizer N-P-K ratings are also ratios, as is the measurement of teaspoons per gallon.
Parts per million is most often alternately expressed as milligrams per liter because it's so easy to convert due to the efficiency of the metric system: 1000 milligrams = 1 gram and 1000 grams of water = 1 liter; 1 thousand x 1 thousand = 1 million; voilá- parts per million.
Fortunately, the "parts" in "parts per million" are generic. It can be parts of a teaspoon just as easily as it can be parts of a gram. N-P-K ratios are also generic expressions of percentage, or parts per hundred. Unfortunately, 1 gallon does not equal 1 thousand teaspoons; it takes 768 teaspoons (or 256 tablespoons) to equal one gallon. But by knowing this, one ratio can be converted into the terms of another ratio, which is what the formulas above do.
Remember:
Before relying on these formulas to fertilize your grow, you should be absolutely aware that N-P-K ratings don't necessarily precisely describe the amount of each nutrient in the fertilizer, but instead describe the minimum amount of nutrient to be found, as explained in Mr.Ito's excellent FAQ on the subject.
The only way to know for certain the ppm of your fert mix solution is to measure it's EC, with an electronic TDS meter as you mix it. If this isn't possible, at the very least try to use only high-quality fertilizer brands with reputations for their accuracy and consistency of their analyses and products.
Author: Don'tTreadOnMe