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What is the difference between PPM, EC, TDS, DS and CF?

Smokin Moose

Fallen Cannabis Warrior
What is the difference between PPM, EC, TDS, DS and CF?

EC, TDS, DS, CF, PPM, Excerpted from Chapter Five, Indoor Marijuana Horticulture, The Indoor Bible

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.

START BOX
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.

Source: Jorge Cervantes
 
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