JustSomeGuy

From what I've read, these are both scales we can use to measure the strength of the nutrient solution, but I was wondering if one was more accurate or useful than the other. Or can one scale do something that the other can't?

BaadPuTthyKat

Hi there & welcome JSG

I tend to agree with the article I have lifted & pasted for you. It's By a Mr Hempseed I believe? Kat


EC, TDS, DS, CF, PPM

Pure distilled water has no resistance and conducts no electrical current. However, when impurities are added to pure distilled water, it conducts electricity. Your water analysis will indicate the impurities or dissolved solids found in household tap water. These impurities conduct electricity. For instance, when you add fertilizer to pure water, the EC climbs.

TDS stands for Total Dissolved Solids. This is just one of the ways to arrive at EC, Electrical Conductivity. EC is the most consistent measure of gross nutrient solution strength.

Nutrient (salt) concentrations are measured by their ability to conduct electricity through a solution. Dissolved ionic salts create electrical current in solution, the main constituent of hydroponic solutions is ionic salts. Several scales are currently used to measure how much electricity is conducted by nutrients including: EC = Electrical Conductivity, CF = Conductivity Factor, PPM = Parts Per Million, TDS = Total Dissolved Solids and DS = Dissolved Solids. Most American growers use PPM, to measure overall fertilizer concentration. PPM is not as accurate, nor consistent as EC, to measure nutrient solution strength.

The difference between EC, CF, PPM, TDS and DS is more complex than originally meets the eye. Different measurement systems all use the same base, but interpret the information differently. First let’s start with EC, the most accurate and consistent scale.


EC = Electrical Conductivity

CF = Conductivity Factor,

PPM = Parts Per Million,

TDS = Total Dissolved Solids,

DS = Dissolved Solids,

END BOX

EC is measured in: (a) Milli-siemens per Centimeter (MS/CM) or (b) Micro-siemens per Centimeter (US/CM). One Micro-siemen/CM = 1000 Milli-siemens/CM.

PPM testers actually measure in EC and convert to PPM. Unfortunately the two scales (EC and PPM) are not directly related. Each nutrient or salt gives a different electronic discharge reading. To overcome this obstacle, an arbitrary standard was implemented which assumes "a specific EC means equates to a specific amount of nutrient solution". Consequently, the PPM reading is not precise at all, it is only an approximation, a ball park figure!

It gets worse! Nutrient tester manufacturers use different standards to convert from CF to the PPM reading.

1. Hanna 1 MS/CM = 500 PPM

2. Eutech 1 MS/CM = 640 PPM

3. New Zealand Hydro. 1 MS/CM = 700 PPM

PPM recommendations are inaccurate and confusing! To help you through this confusion, please see the following chart.

1 MS/CM = 10 CF e.g. 0.7 EC = 7 CF.

Conversion scale from PPM to CF and EC.

EC Hanna Eutech Truncheon CF

MS/CM 0.5 0.64 0.70 0

0.1 50 PPM 64 PPM 70 PPM 1

0.2 100 PPM 128 PPM 140 PPM 2

0.3 150 PPM 192 PPM 210 PPM 3

0.4 200 PPM 256 PPM 280 PPM 4

0.5 250 PPM 320 PPM 350 PPM 5

0.6 300 PPM 384 PPM 420 PPM 6

0.7 350 PPM 448 PPM 490 PPM 7

0.8 400 PPM 512 PPM 560 PPM 8

0.9 450 PPM 576 PPM 630 PPM 9

1.0 500 PPM 640 PPM 700 PPM 10

1.1 550 PPM 704 PPM 770 PPM 11

1.2 600 PPM 768 PPM 840 PPM 12

1.3 650 PPM 832 PPM 910 PPM 13

1.4 700 PPM 896 PPM 980 PPM 14

1.5 750 PPM 960 PPM 1050 PPM 15

1.6 800 PPM 1024 PPM 1120 PPM 16

1.7 850 PPM 1088 PPM 1190 PPM 17

1.8 900 PPM 1152 PPM 1260 PPM 18

1.9 950 PPM 1260 PPM 1330 PPM 19

2.0 1000 PPM 1280 PPM 1400 PPM 20

2.1 1050 PPM 1344 PPM 1470 PPM 21

2.2 1100 PPM 1408 PPM 1540 PPM 22

2.3 1150 PPM 1472 PPM 1610 PPM 23

2.4 1200 PPM 1536 PPM 1680 PPM 24

2.5 1250 PPM 1600 PPM 1750 PPM 25

2.6 1300 PPM 1664 PPM 1820 PPM 26

2.7 1350 PPM 1728 PPM 1890 PPM 27

2.8 1400 PPM 1792 PPM 1960 PPM 28

2.9 1450 PPM 1856 PPM 2030 PPM 29

3.0 1500 PPM 1920 PPM 2100 PPM 30

3.1 1550 PPM 1984 PPM 2170 PPM .1

3.2 1600 PPM 2048 PPM 2240 PPM 32



Every element in a multi-element solution has a different conductivity factor in these approximate measurements. Pure water will not conduct electrical current, but as elemental salts/metals are added, electrical conductivity increases proportionately. Simple electronic meters measure this value and interpret it as total dissolved solids (TDS). Nutrient solutions used to grow marijuana generally range between 500 and 2000 parts per million (PPM). If the solution concentration is to high, the internal osmotic systems can reverse and actually dehydrate the plant. For general purpose, try to maintain a moderate value of approximately 800 to 1200 PPM. Nutrient solution concentration levels are affected by nutrient absorption by roots and by water evaporation. The solution weakens as plants use nutrients, but water also evaporates from the solution, which increases the nutrient concentration. Adjust the concentration of the solution by adding fertilizer or diluting with more water.

Super Size Secret: Use an EC meter to check the overall strength of your nutrient solution. EC is the most consistent measure of overall solution strength.

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grass_hopper

Many pens measure in TDS and then convert to EC using a conversion factor. From my recent shopping experience for an EC/TDS pen, EC is much more common amongst our friends across the pond, where TDS is pretty common here in the states.

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hawk420

Yeah what he said


from my expierence and what little it is you can get by with just EC, CF and PPM.
I think football...know your 7 times table that is how i convert PPM-->CF

for EC just put that decimal point in there...same number as CF but *.* format

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penguin

Close, but backwards. All measures of dissolved solids actually measure electrical conductivity (in Siemens). TDS meters then convert this value to an approximate PPM; different manufacturers use different conversion factors.

EC is more accurate.


penguin

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JustSomeGuy

Thanks for the responses guys. I had one more question pertaining to the whole ppm/ec thing. Within time, is ppm/ec suppose to go down because the nutrients are being used by the plants or does it just stay the same? I have a Hanna ph,ec,ppm tester and when I test it, i've noticed that there is very little change in the ppm's(about 5 ppm). My plants are 19 days old and doing good under two 400 watt metal halides. The plants are about as big as the picture i attached from a previous grow but they are not the same ones I am talking about. Is it normal for the ppm's to stay about the same at that stage?

Attached Thumbnails

 

hawk420

if your PPM goes up it means your plants are using more h2o than nutrients and if they go down they are using more nutes than water.

If your ppm is constant than your system is balanced.

this explains it here

this is in CF but same applies for EC or PPM

very little change in PPM is good. and just pay close attention to the very tippy tips of the leafs and watch for any yellowing.

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JustSomeGuy

Thats interesting Hawk, I didn't know that. One last question just in case, what causes a plant to use more h2o than nutes and vice versa? How do you fix that problem just in case I run into it.

BaadPuTthyKat

JSG,

Thats a big question with lots of answers. People devote their life's work to just a small aspect of that scope. Some simple plant biology books will help you understand more. Its too big for one evening, but watching your plants before & after feeding will help. Kat

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hawk420

not sure what causes the plant to use more h2o, I think it is that it just doesn't need as many nutes that are in the solution.

If you PPM is rising then your can top of your res with plain Ph'd water and will bring your ppm down. If it dosnt bring it down to where it needs to be then you can pump out some of the solution in the res and refill with plain Ph'd water till the ppm is where you need it. I have rarley had to do that. Or you can always dump res and start over, but I usually just top of with Ph'd water. Then replace res once every 7-10 days

Ex:

right now i am running 1000 PPM every day they drink about 2 gallons of water. Today when i got home the ppm was 1100. I topped off the 2 gallons they drank and brought ppm to 900.

Another Ex:

sometimes they drink 2 gallons and the ppm will stay at 1000 then i top off 2 gallons they drank with plain ph'd water which drops ppm to 850 or so. I will then add very little nutes to get back to 1000.

make sense??

PS. I had no idea about this either till i joined HC.com

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