EC vs PPM

[dedust]

happy new year!

sorry for the noob question, but can someone explain which is better to use when mixing nutes?

it seems most people use ppm, but i see people referring to ec once in a while.

make it your resolution to help a noob! haha...

 

[ent]

I posted this before, so i'll repaste. Hopefully this clears up the confusion.

TDS is measured in PPM.

EC is measured in either µS (MicroSiemens) or mS (MilliSiemens). 1000µS is equal to 1mS.

In the USA we typically use PPM, however internationally µS and mS are the preferred measurements.

The conversion from EC to TDS is not cut and dry. The reason is that different meters use different conversion factors. The TDS is based off of the EC reading. Therefore, NOT ALL TDS METERS WILL GIVE THE SAME PPM READING.

The most common conversion factors are:

µS * 0.5
µS * 0.7

For instance. A EC reading of 1.52 mS would equal 1520 µS.
Meters using the (0.5) conversion will give a reading of 760 PPM. 1520 * 0.5 = 760
Meters using the (0.7) conversion will give a reading of 1064 PPM. 1520 * 0.7 = 1064

Meters that use the 0.5 conversion are:
Hanna Primo
Tri-Meter
Hanna HI981504

Meters that use the 0.7 conversion are:
Hanna HI 9813-0
Hanna HI 9813-6
Hanna HI 983301N
Hanna HI 983311

Meters that are adjustable are:
Hanna HI98129
Hanna HI98311
Hanna HI981404
Hanna HI981404N
Oaktron Meters

The Blue Lab Truncheon TDS/EC meter will display in PPM using both 0.5 and 0.7 factors and also display the EC.

 

[dedust]

wow! thanks for that ent. makes sense now...

so, does it matter which you use? are there preferences, or is it just what part of the world you're from? thanks again dude.

 

[Seamaiden]

One thing that's important to remember (there are a few things, actually) is that TDS and ppm are calculated from uS (microSeimens, can't be arsed to get ent's special character). That's why the conversion factor is so important.

Another thing is that certain types of molecules simply cannot be measured by electrical conductivity.

 

[dedust]

One thing that's important to remember (there are a few things, actually) is that TDS and ppm are calculated from uS (microSeimens, can't be arsed to get ent's special character). That's why the conversion factor is so important.

Another thing is that certain types of molecules simply cannot be measured by electrical conductivity.

does that mean it's better/more accurate to use ppm? or am i completely missing the point? haha...

 

[Nobodynobody]

PPM. Dont wast your time with EC unless you got rockwool or some kind of reason... salt build up...

 

[homebrew420]

does that mean it's better/more accurate to use ppm? or am i completely missing the point? haha...

nope. Plenty of comercial growers use EC. There is not a "better form of measuring the nutrient level. They are both accurate as they can be...if that makes sense? Simply different ways of measuring.

http://www.hydroponics.net/learn/debate_over_ec_and_tds.aspp

peace

 

[ent]

does that mean it's better/more accurate to use ppm? or am i completely missing the point? haha...

The meters are actually measuring the electrical conductivity with a unit of measure known as microsiemens. Then they use a mathematical conversion to estimate what the total dissolved solids would be in the unit of measure known as parts per million.

Some meters convert using a factor of 0.5 and some use a factor of 0.7. As a result, the exact same water measured with two meters that use different conversion factors will give you a reading in parts per million that are different, while the reading in EC will be the same.

For example, if you tested the same water that has an EC of 1.0 with meters that use different conversion factors they will both read an EC of 1.0 but one meter will say 500 PPM while the other will say 700 PPM.

It is this reason that I do all of my measurements in EC.

 

[dedust]

The meters are actually measuring the electrical conductivity with a unit of measure known as microsiemens. Then they use a mathematical conversion to estimate what the total dissolved solids would be in the unit of measure known as parts per million.

Some meters convert using a factor of 0.5 and some use a factor of 0.7. As a result, the exact same water measured with two meters that use different conversion factors will give you a reading in parts per million that are different, while the reading in EC will be the same.

For example, if you tested the same water that has an EC of 1.0 with meters that use different conversion factors they will both read an EC of 1.0 but one meter will say 500 PPM while the other will say 700 PPM.

It is this reason that I do all of my measurements in EC.

thanks for the info. does that mean that ppm is more accurate in the sense that ec is only read to the first decimal (i think)?

 

[CalcioErba2004]

if you want accuracy then forget PPM. The measurements are in made in EC and then converted to PPM by a mathematical equation. EC measures anything in the water, period. 0 EC water is pure H2O, a perfect insulator. If it has anything in it at all it will conduct electricity and show up on an EC meter. How sensative(How many decimals) the meter is depends on how much money you have. The more sensative the meter is the more money it will cost.

 

[Seamaiden]

does that mean it's better/more accurate to use ppm? or am i completely missing the point? haha...

It's actually much more accurate to measure electrical conductivity, but ONLY if you're using chemical nutrients. EC cannot be accurately measured with many, if not most, organic compounds and this is due specifically to the nature of the molecules. Measuring organic compounds is complicated and extremely, extremely expensive.

There are other conversion factors, too. I haven't seen which meters use what I call "the screwy conversion factors" (something like... .635, a really screwy number).