PJ Diaz
Well-Known Member
I guess I don't understand what you are trying to do. PPM to EC is a simple conversion.
Nutrient PPM Question
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Norville Rogers
Member
@PJ Diaz
It's not talked about much, but the long story short is with substances the elemental ppm is easy to find out with what we're given. The problem is the only way to measure the actual ppm is with lab analyses. So, we use "cheaper" meters to measure the same thing through EC that is the electrical conductivity of the mixtures different elements and then with a basic calculation (.500 or the 700 scale) to "determine" the ppm, wich is actually TDS, the total dissolved solids. The problem is the elements all give off a different "charge" depending on the ie: water quality. Add RO water to the calculations and there's no buffer that can hinder the results even more. PPM and EC are calculated through different means and therefore EC doesn't usually line up with the actual ppm numbers. We are trying a middleman attack to guess the EC (what our meters say) properly according to the actual ppm numbers. I know, it's weird but true.
A quick example, actual elemetal ppm of 5 grams a gallon mix is 400 ppm that we both mix, my meter says 550, yours says 600. We can both guage our systems by our meter numbers, but the real number would be 400 ppm no matter what our meters say. I personally have 3 meters that all show slightly different numbers of the same mix. When people say they use 1100 ppm i don't know if they mean the real ppm, tds their meter spits out, and wich scale their meter uses; EC basically the same thing.
It's not talked about much, but the long story short is with substances the elemental ppm is easy to find out with what we're given. The problem is the only way to measure the actual ppm is with lab analyses. So, we use "cheaper" meters to measure the same thing through EC that is the electrical conductivity of the mixtures different elements and then with a basic calculation (.500 or the 700 scale) to "determine" the ppm, wich is actually TDS, the total dissolved solids. The problem is the elements all give off a different "charge" depending on the ie: water quality. Add RO water to the calculations and there's no buffer that can hinder the results even more. PPM and EC are calculated through different means and therefore EC doesn't usually line up with the actual ppm numbers. We are trying a middleman attack to guess the EC (what our meters say) properly according to the actual ppm numbers. I know, it's weird but true.
A quick example, actual elemetal ppm of 5 grams a gallon mix is 400 ppm that we both mix, my meter says 550, yours says 600. We can both guage our systems by our meter numbers, but the real number would be 400 ppm no matter what our meters say. I personally have 3 meters that all show slightly different numbers of the same mix. When people say they use 1100 ppm i don't know if they mean the real ppm, tds their meter spits out, and wich scale their meter uses; EC basically the same thing.
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PJ Diaz
Well-Known Member
TDS is the ".500 scale". I hear what you're saying, but I think you are chasing semantics and minutia.
Norville Rogers
Member
I agree PJ. I already did the work though 
An EC meter measures the conductivity and then converts that value to indicate what concentration of sodium chloride (the 500 scale) or potassium chloride (the 700 scale) you would need to have to have that same level of conductivity.
There is no discrepancy
EC is not calculated. Electrical conductivity meters measure electrical conductivity and express it in microsiemens blah blah blah. Once the electrical conductivity has been measured, that value can be expressed so as to indicate how many parts per million of total dissolved solids would be needed to carry that same charge. An EC meter will convert the EC reading and display it on the 500 scale or the 700 scale. The 500 scale indicates the PPM of a solution of sodium chloride; the 700 scale indicates how many parts per million would be needed it the dissolved solid was potassium chloride. There's no issue of things not lining up - it's a straight conversion.
This article from Bluelab explains it really well.
There is no discrepancy
You can't measure EC of RO because there are 0 dissolved solids so there's nothing to carry the current. RO water only makes it difficult to measure because RO water has nothing to carry the current so the EC is 0.
EC is not calculated. Electrical conductivity meters measure electrical conductivity and express it in microsiemens blah blah blah. Once the electrical conductivity has been measured, that value can be expressed so as to indicate how many parts per million of total dissolved solids would be needed to carry that same charge. An EC meter will convert the EC reading and display it on the 500 scale or the 700 scale. The 500 scale indicates the PPM of a solution of sodium chloride; the 700 scale indicates how many parts per million would be needed it the dissolved solid was potassium chloride. There's no issue of things not lining up - it's a straight conversion.
This article from Bluelab explains it really well.
Norville Rogers
Member
@Delps8
Everything you said i knew and made sense so i agree with you. The one part i'm not sure of 100% was regarding what you said about RO; i realize plain RO has zero charge but once i add nutrients IMO it shouldn't matter and the readings would be measuring the salts i added that have a charge. Unless RO interfered with those readings compared to if i used tap and deleted the base water ppm i agree with what you said and afaik never said differently. Once again my ppm conversions all match that of hydrobuddy but after i mix a batch with RO and take readings the numbers are all higher on the meters (all on .500 scale; 2 bluelabs and a HM). Thats the part we can't figure out, and hydrobuddy itself has adjustments for this very thing wich i believe is the various elements carry a unique EC charge from one another, it's all estimation.
Everything you said i knew and made sense so i agree with you. The one part i'm not sure of 100% was regarding what you said about RO; i realize plain RO has zero charge but once i add nutrients IMO it shouldn't matter and the readings would be measuring the salts i added that have a charge. Unless RO interfered with those readings compared to if i used tap and deleted the base water ppm i agree with what you said and afaik never said differently. Once again my ppm conversions all match that of hydrobuddy but after i mix a batch with RO and take readings the numbers are all higher on the meters (all on .500 scale; 2 bluelabs and a HM). Thats the part we can't figure out, and hydrobuddy itself has adjustments for this very thing wich i believe is the various elements carry a unique EC charge from one another, it's all estimation.
"Once again my ppm conversions all match that of hydrobuddy but after i mix a batch with RO and take readings the numbers are all higher on the meters (all on .500 scale; 2 bluelabs and a HM).
I don't know what "my ppm conversions" means. Do you mean that PPM readings from the EC meter?
I don't know what "my ppm conversions" means. Do you mean that PPM readings from the EC meter?
Billy the Mountain
Well-Known Member
You're confusing the derived PPM reading from an EC meter to the elemental PPM of a nutrient mix.
They're not the same
Kassiopeija
Well-Known Member
how can you derive a ppm reading from an EC meter?
Yes, that sounds like the source of the confusion.
I suspect that BTH is referring to the fact that the PPM is derived (by the meter) from the EC value.
Billy the Mountain
Well-Known Member
Press the button on the meter which changes the displayed scale.
The meter only measures conductivity, the other scales are derived from that value.
Yup, it's a derived, somewhat arbitrary value. The TDS (500) scale is only an accurate representation of ppm for NaCl
700 scale is based on KCl
Confusion arises when people use the displayed ppm value as representative of the actual PPMs in their nutes; which it's not.
Key point - "Once again my ppm conversions all match that of hydrobuddy but after i mix a batch with RO and take readings the numbers are all higher on the meters (all on .500 scale; 2 bluelabs and a HM)."
The elemental PPM is the sum of the PPM of the individual chemicals, based on the values that the manufacturer prints on the container. The values are the minimum value, so the actual values may well be greater than those that are printed. Second, the chemicals are bound together by an inert but soluble binder. The impact of those two factors will pretty much ensures that the PPM won't match the PPM value that the EC meter calculates after it does the EC readings.
The two numbers each have their own use but, as you've seen, they don't match up.
"conversions" is the word that threw me off. I thought you were referring to the EC meter converting its reading into PPM.
Norville Rogers
Member
I meant calculate rather than convert in that case, my bad. To me the elemental values are static for lack of a better term, and the EC is somewhat variable and guesstimated and i agree with what you said. I was trying to relay similar things earlier in thread. There are so many possible product combinations with god knows what additives in them that this is guess based science with what we're given at best, but the elemental ppm is a good baseline for my ratios and tinkering, and then adjusting the strength % while maintaining my target ratio based on what the EC does throughout the week and what the plants tell me.
"I meant calculate rather than convert in that case, my bad." - understood.
"To me the elemental values are static for lack of a better term, and the EC is somewhat variable and guesstimated" - good way to put it.
"There are so many possible product combinations with god knows what additives in them that this is guess based science with what we're given at best," - And then add in the other variables. My Bluelab EC pen and my monitor are both within the stated tolerance of EC 0.1. With a standard solution of 1385, the monitor reads 1400 while the pen reads 1340. So they're 60 PPM apart but both are "accurate".
"but the elemental ppm is a good baseline for my ratios and tinkering, and then adjusting the strength % while maintaining my target ratio based on what the EC does throughout the week and what the plants tell me." - ah, hats off to you.
I used bottled nutes for a couple of grows and threw all them away. I'm finishing my first grow using Jack's 3-2-1 (I don't use the "1") but I've only changed it once during the grow, to get a little more manganese in the res.
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