Understanding EC, CF, and PPM in hydroponics.

Getting nutrients right is the difference between a successful grow and a limited production – or complete failure. On my first attempt at hydroponics, I could get my plants to grow foliage, but fruit production fell short. My tomatoes would not set fruit, plants began to die, and I fluctuated between nutrient deficiencies and toxicity.

I followed the general recommendations on the nutrient instructions, but some plants have very specific needs. Some plants can only tolerate low levels of nutrients, while others are nutrient hogs. To make matters worse, I had both types of plants in the same system. In error, I figured a general grow solution would work for both. It turns out, it worked for neither.

I had good lighting and a good working system, but the wrong PH and poor nutrient balance. In order to have an effective system, you must have the right nutrients at the right levels, and the proper PH levels. Balance the nutrients, and then balance the PH.

This article will focus on balancing the nutrients. To learn about PH, see my article on Getting the right PH.

For several months I scrapped my hydroponic system and stayed with soil. However, after seeing all the success others were having on the internet, I set out to find out where I went wrong. I then discovered conflicting information. Lots of conflicting information. An example of this was a forum discussion where someone was having trouble with toxicity in their peppers. One person recommended never going beyond 900 PPM (Parts Per Million) of nutrient for peppers. Another forum stated that the minimum solution should be 1260 PPM.

Then people started talking about EC levels, TDS, CF and all these other acronyms. I had no idea where to start in deciphering it all. If you are new to hydroponics, you may have had similar questions. Rather than complicating the process with endless details, I’m going to break it down in the simplest terms. Anyone who wants to go deeper can find a plethora of information on the internet.

Let me start by explaining that there are two main standards of measuring nutrient levels. There are more than these standards, but only two that you’ll commonly come across. Before explaining these standards, let’s define the acronyms you’ll come across for clarity sake.

PPM – Parts Per Million. For every million parts water, the PPM tells you how many parts of non-water impurities are in the water. By impurity, I am referring to anything that isn’t pure water. Pure water does not conduct electricity. It’s the dissolved salts in the water that conduct electricity.

TDS – Total Dissolved Solids. This refers to the impurities in the water. Whatever is dissolved in the water is a dissolved solid. That impurity could be anything from Chlorine to the nutrients you are adding, to anything else the water has absorbed and carried into your reservoir.

EC – Electrical Conductivity. All nutrient ions in the water carry an electrical charge. This is how nutrient meters measure and estimate the PPM. EC is charted with a decimal point. Most EC meters will measure between 0.2 and 3.6 EC.

CF – Conductivity Factor. CF is the same as EC but without the decimal.

0.2 EC equals 2 CF.

1.8 EC equals 18 CF.

Just remove the decimal point from the EC and you have the CF rating.

Here is where one of the great areas of confusion arises. EC is primarily an American standard and CF is a European standard. While it is easy to convert EC to CF and vice-versa, it isn’t as easy to convert the CF parts per million to the EC parts per million. For example, 2.0 EC is 1000 PPM. 2.0 EC equals 20 CF, but the European standard of PPM isn’t 1000 PPM, but 1400 PPM.

Now you see where the confusion comes from. So when getting advice from a book, forum, or other source, it’s important to know whether they are referring to CF or EC. In my earlier example, this is why one person said to never go over 900 PPM and the other source said 1260. Both are right. One was in EC and the other in CF.

It’s confusing, I know. But just remember that all you need to do is convert EC to the American standard of PPM and CF to the European. Here is an easy formula.

Multiply EC x 700 to get the PPM

Multiply CF x 500 to get the PPM

So when do you use CF, PPM, or EC? It all depends on how your meter displays results. You may need to know this information if you are getting advice from a book, the web, or another resource. Regardless of how the nutrient levels are presented for the plant you are growing, you’ll want to be able to convert it into information you can use and measure.

Another thing to consider is that the only way to determine the PPM with 100% accuracy is by chemical analysis. Unless you live in a science lab, that isn’t going to be practical. The total dissolved solids (TDS) in the water will be affected by anything that encounters your water. PPM meters give a very good estimate of the total dissolved solids, but if you have hard water or are recycling old water, the PPM accuracy will be affected.

If you live in an area that has hard water, measure the PPM before adding solution and factor that number into your measurements.

Also, limit how long you use water in your hydroponic system. If your plants are just seedlings, you can get away with reusing the water for a month or so. As they mature and begin absorbing more nutrients, change the water every two weeks. During heavy fruiting, change the water weekly.

The PPM rating estimates how much nutrient is in the water, but not what nutrients are available. Once the plants have been drawing from the solution, they will be taking up the nutrients needed for each plant, and the nutrients left behind are the ones not needed or less needed. In this case, you can have the recommended PPM but still starve your plants. It’s impossible to tell what nutrients remain and which are used, so changing water is essential.

Raising the PPM to make up for nutrient deficiencies will not work. Having too much of any one nutrient will create toxicity. You need a solution balanced for what you are growing. Let me give an example.

squash deficiencysquash nutrient

The picture to the left is a squash plant showing signs of toxicity. Notice the deformity in the leaves. After replacing the water with a fresh solution, the same plant now shows healthy new growth. The more productive the plant becomes, the more important it is to change the solution regularly.

Below is a chart that gives suggested levels for each type of vegetable in EC, CF, and PPM. You can download this in PDF format by clicking here.

Plant EC PPM x 500 CF PPM x 700
Asparagus 1.4 – 1.8 700 – 900 14 – 18 980 – 1260
Basil 1.0 – 1.4 500- 700 10 – 14 700 – 980
Beans 1.8 – 2.5 900 – 1250 18 – 25 1260 – 1750
Beets 1.4 – 2.2 700- 1100 14 – 22 980 – 1540
Blueberry 1.8 – 2.0 900 – 1000 18 – 20 1260 – 1400
Broccoli 1.4 – 2.4 700 – 1200 14 – 24 980 – 1680
Cabbage 1.4 – 2.4 700 – 1200 14 – 24 980 – 1680
Carrot 1.4 – 2.2 700 – 1100 14 – 22 980 – 1540
Cauliflower 1.4 – 2.4 700 – 1200 14 – 24 980 – 1680
Celery 1.5 – 2.4 750 – 1200 15 – 24 1050 – 1680
Chives 1.2 – 2.2 600 – 1100 12 – 22 840 – 1540
Corn (Sweet) 1.6 – 2.4 800 – 1200 16 – 24 1120 – 1680
Cress 1.2 – 2.4 600 – 1200 12 – 24 840 – 1680
Cucumber 1.6 – 2.4 800 – 1200 16 – 24 1120 – 1680
Eggplant 1.8 – 2.2 900 – 1100 18 – 22 1260 – 1540
Endive 0.8 – 1.5 400 – 750 8 – 15 560 – 1050
Garlic 1.4 – 1.8 700 – 900 14 – 18 980 – 1260
Lettuce – Loose Leaf 0.3 – 0.8 150 – 400 3 – 8 210 – 560
Lettuce – Iceberg 0.6 – 1.4 300 – 700 6 – 14 420 – 980
Melons 1.0 – 2.2 500 – 1100 10 – 22 700 – 1540
Mint 1.0 – 1.4 500 – 700 10 – 14 700 – 980
Mustard 1.2 – 2.4 600 – 1200 12 – 24 840 – 1680
Okra 2.0 – 2.4 100 – 1200 20 – 24 1400 – 1680
Onion 1.8 – 2.2 900 – 1100 18 – 22 1260 – 1540
Parsley 0.8 – 1.8 400 – 900 8 – 18 560 – 1260
Parsnips 1.8 – 2.4 900 – 1200 18 – 24 1260 – 1680
Peas 1.4 – 1.8 700 – 900 14 – 18 980 – 1260
Peppers 1.8 – 2.8 900 – 1400 22 – 28 1260 – 1960
Pumpkin 1.4 – 2.4 700 – 1200 14 – 24 980 – 1680
Radish 1.2 – 2.2 600 – 1100 12 – 22 840 – 1540
Sage 1.0 – 1.6 500 – 800 10 – 16 700 – 1120
Spinach 1.8 – 3.5 900 – 1750 18 – 35 1260 – 2450
Squash 1.8 – 2.4 900 – 1200 18 – 24 1260 – 1680
Strawberry 1.8 – 2.5 900 – 1250 18 – 25 1260 – 1750
Thyme 1.2 – 1.6 600 – 800 12 – 16 840 – 1120
Tomato 1.8 – 2.8 900 – 1400 22 – 28 1260 – 1960
Turnip 1.8 – 2.4 900 – 1200 18 – 24 1260 – 1680
Watercress 0.4 – 1.8 200 – 900 4 – 18 280 – 1260

Eddie Snipes 2012

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Understanding EC, CF, and PPM in hydroponics. — 4 Comments

  1. Pingback: Watch the PH in your Hydroponic System | Suburban Vegetable Gardening

  2. A lot of very importao. I can identify. I have only now begun to work on my hydroponic system. All this information has been helpful.

  3. I was just looking at buying a meter to measure ppm and was lost in the sea of info, thanks for clarifying the terms and their equivalents.

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