Here's a link to a dandy little (actually HUGE--which is why I don't just copy and past it right here) chart:

http://www.gardeningcamp.com/thewiki/index.php/Hydro/ECPHCharts

These are very conservative values, in my opinion. Like I've said in other parts of this forum, I grow lettuce at an EC of 1.8 and pH of 6.3. At least we agree on the pH!

I screwed up! :O(

Click the "back" button and look for a post that says "Bluelab Truncheon Limits". I was researching the topic of EC-level Charts and contacted Bluelab. They sent me one by email and I put a link to it in a reply to a post there.

OK, just in case . . . here's another list: pH/PPM/CF for Various Vegetables

if you don't know the conversion factor they are using those lists are useless.
my two cents

Bob

Conversion factor?

Me thinks life has become too complicated. Neither of the sites I found the tables at said anything about "conversion factors" and one was directly from Bluelab in Australia.

If you could explain a bit on what you mean by conversion factors, maybe the rest of us could better use the information in the tables. I was going to post each of those tables on my Web page for everyone to see; now I'm skidish!

:O(

I've got news for you guys: There is no such thing as a "conversion factor" in conductivity tests. There is no relation between ppm and CF (or EC, or S). It simply does not exist as a reproducible measure in our field of interest.
If (big "if") you have a solution of a single salt, then you can find a relationship between ppm and conductivity, but only for a single salt and only for that salt, and never for a mixture of salts.
In hydroponics you should avoid dealing in ppm. It's very confusing. Measure CF (or EC, or µS)instead. At least we all know what that means.

Well said, greystoke. Thank you.

That having been said, I should think I will be getting back to the business of growing veggies and not worrying about so much of the technical stuff. I "am" going to do a month of "testing" using R/O water instead of tap water to see if it makes any difference, but that's about as "techie" as I hope to get just now.

Thanks again.

Actually, there is such thing as a conversion factor. All of those numbers are representations or conversions of EC. CF = EC x 10. PPM is EC x 500 or x 700 depending on which you use. I agree with greystoke, except I would prefer everyone use EC since that is the only value actually measured. The rest are conversions of EC, so why use them if you know EC?

I have the usual problem with recommended EC published by nutrient manufacturers.......remember what they are selling?

Capsicum recommendation is 1260-1540 ppm at 6.5Ph. Ppm is high by a factor of 6 to 10. I have 10 years of data on this subject.

joe.jr317 wrote:
All of those numbers are representations or conversions of EC. CF = EC x 10. PPM is EC x 500 or x 700 depending on which you use.
Yeah, but what does it mean? On some of these meters you can choose almost ANY conversion number. It may have a meaning to you and the way you do things, but it means litle to others.

Greystoke, I think we may be misunderstanding one another. My point was that even CF is a conversion of what is measured and people, especially manufacturers of nutes, should only use EC since it's the only thing measured. PPM is not only inaccurate, but unclear when considering there are two different scales and the one used is rarely indicated in nutrient instructions, which I believe was the point aerobobponics was making. All three numbers beyond EC are conversions. Period. Whether accurate or not, he was right that they are conversions of a single number. The nomenclature (ppm) is what is wrong, not that these are conversions.

In regard to your "It may have meaning to you. . ." statement: If an individual isn't willing to learn a bit about EC and what the information means, they shouldn't be using the truncheon in the first place. I use an infrared camera regularly because I know how to interpret the data. I wouldn't pay a ton of money for the camera if I didn't want to learn to interpret the data. That would be stupid. I think that applies to any measuring equipment.

Let me clarify further why I don't like PPM numbers and why they are not accurate. Not all elements a plant uses have the same conductivity factor. Therefore, if you are using a vegetative formula and switch to a bloom formula from a commercial manufacturer you will find that the EC is different even if you use the same exact amount. I don't know the ec of each element, but I do know they vary. That means that EC can't possibly give you an accurate reading of PPM. I was agreeing with greystoke on that. But, EC can affect whether water is taken up by a plant or whether nutrients are available at certain pH levels or not. I am also pretty sure that is why you often see two numbers for plants on some charts. They have a grow ppm and a bloom/fruit ppm. It's based on you actually making the change from one product to the other and doesn't apply if you don't. It's also why sometimes you will find ppm recommendations different from one manufacturer of nutes to another. All these variables are a perfect reason one should simply follow the manufacturers directions at first and adjust by observation rather than use a generic chart. Record pH and amount of additives (pH UP or DOWN) if pH needs adjusted. Record EC on the initial mixture prior to use so you establish a baseline. It doesn't matter if you have 1.8 EC or 2.4 EC. The contents of the nutes will determine the EC and manufacturers often have proprietary variables. There is no magic EC and nutrient uptake occurs over a wide range. If a ppm chart shows tomatoes needing more ppm's than lettuce, use the proportion of difference and apply it. Then record your baseline data. The entire point of measuring EC is to establish baseline so you know to stick with it or know what you have adjusted from and can determine what works best for your plants. I think that very simple point is the most missed point and also the reason the thread was started in the first place. A chart is only as good as the reader's ability to interpret the data and understand it's limitations. Since each manufacturer has different content to an extent, it would be helpful if they used EC to tell you what the measurement should be if you follow their directions. This would help to ensure you properly mixed the solution from the get go and would let you know if you might have caused a lock out issue. If you make your own nutrient solutions, you should be taking notes of what the EC is on certain mixtures and at certain pH and temperatures (which also can affect EC). There is no substitute for experience when it comes to learning to do something right. This last paragraph was my input in regard to the original question.

Well said. I think I actually did misunderstand you. Sorry.

This thread is worth a bump!

People, forget the term PPM even exists unless you're mixing your own solutions from individual salts. There is no scientifically valid conversion of EC to "PPM" - at least not to viably represent ion concentrations from EC. There are commonly used factors, but why bother?! Who was the idiot that started this pseudo-science nonsense? Give it up! There is a valid estimate of TDS from EC, but once again, why bother?

EC is the amount of conductivity your solution has. Hence the word "conductivity" in EC. Essentially it is not as accurate as people think but still gives a rough approximation of how strong your solution is. As for ppm, well, I think it is bogus to think that using an electrical current we can figure out how many parts per million of nutrients are in water. Not with a truncheon meter at least. I believe EC is still the way to go too and the best part is that you don't have to worry about some silly "conversion factor."

PPM (Parts Per Million)
EC (Electrical Conductivity)
TDS (Total dissolved Solids/Salts)

None are better than the other, they all do the same thing. They are all just a relative strength of the elements (nutrients/ions) in the nutrient solution. The key word is "relative." But in the long run, none are exact measurements to go by. Unless they can brake it down into individual elements. Not one of these options can do that.

P.S. I realize this is a debate that will probably continue until the end of time. But I have never seen any evidence that points to one over the others. If there were, there wouldn't be so much debate on the subject. Whatever works for you, stick with.

The debate will only go on for people that still haven't, are still trying or will never understand how to use these units and how-, if- and when they correlate.

PPM are typically used when calculating nutrient formulas or if parts per million are a KNOWN based on molecular calculations and chemical formulas. In this case ppm correspond and are the unit and standard in use. Although theoretical and not as 100% exact in real life applications as they should be, it's the commonly used unit and standard in use here.

EC (electrical conductivity) is measured in mS/cm or µS/cm sometimes dS/m and is indeed the ONLY standard that can be considered as a (unique) UNIT when measuring a nutrient solution. It's not a question of if you like it as a unit or if it describes the measurement best, - it's the only valid UNIT there is for the user.

Because TDS aka PPM-meters come in several, mainly 2 standards. They measure electrical conductivity as well and unfortunately use DIFFERENT coefficients to transfer EC to ppm, based either on NaCl ppm of its relative conductivity, - or based on PCl ppm with a relative conductivity. They are not actually meant to measure the total ppm or the total dissolved solids of any nutrient soution, as they CAN'T do that. They can do it theoretically and practically with NaCl or PCl ONLY! Hence, as far as the measurements of nutrient solution is concerned, it is indeed a double BOGUS for the hydroponic user!

The confusion with so called TDS-meters is inevitable, because of these two main standards that are in use,- one using ( still based on EC) a /500 conversion and the other /700 conversion rate. Imagine people in the same community and ¨sphere of influence¨ using imperial gallons and US gallons, (3.78 Liter versus 4.54 Liter) alternatively without being aware of the difference! With the use of two different ppm standards (/500 and /700) there simply is a difference of 20% if there is confusion with standards, or if using recommendations that are transferred to the wrong standard. And that is simply misleading and inaceptable!

One more confusion is very likely to happen, if people are starting to make their own nutrients and eventually come to use PPM as a unit with their calculations and results. If they are not aware of the above facts, they may indeed end up thinking that a TDS-meter using ppm as a unit, would translate their results best with making up nutrient's final concentrations. Well, it doesn't at all translate, as the nutrient solution hasn't the same conductivity factor of either standard (500/700) in use.

There is only one way to achieve knowledge standardisation and avoid confusion here: use ppm as a standard for your nutrient (and molecular weight) calculations - and EC for measuring your final concentration, respectively when making up nutrient solutions!

There is nothing to debate about it, except for people who seem to not want to understand the circumstances nor accept the situation and the analogous facts as they are. If people would finally want to understand instead of debating by principle, this would be such a clear-cut issue! ;-)

I knew that lucas wouldn't be able to resist an opportunity to look smarter than everyone else. True to form, and a whole lot about nothing.

Ok, Say I have all three meters, the readings of 3 different nutrient solutions read;

PPM, 1750
EC, 2.0
TDS, 2500

Now that you know what the readings are, you should be able to tell exactly how much of each of these elements are in the selution.

Nitrogen
Potassium
Phosphorous
Calcium
Magnesium
Sulphur
Iron
Manganese
Copper
Zinc
Boron

So from the PPM,EC and TDS values, what are the levels of each element in each solution? Also what if any other elements are in the solutions. Fact is, you simply cant tell, that was my point. Doesn't mater which you use, they can only tell you the total value, they cant break it down. If someone were to check the readings daily (no mater witch meter they have), it can tell you the relative strength of the nutrient solution. As it increases due to water uptake, increasing the unused nutrient concentration as water level drops. Or depletion, due to the plants taking up the nutrients in the solution. But none of them can tell you what elements are present, or in what quantity's. Again that was/is my point.

"There is nothing to debate about," if you "would finally want to understand instead of debating by principle, this would be such a clear-cut issue!"

Homehydro,
Your "point", that any instrument's readings operating in any "units", modus or standards can't read single elements out of a solution is actually the FIRST LESSON to learn! Which I dropped and ignored indeed, because I actually supposed that at least this part was obvious and well known by all takers on the table.

Although you can't deduce any single element content with either standard or unit nor instrument, - that doesn't make all standards and units equal or equally unqualified. The next level of understanding tells us why EC is the only real unit of all.

Well If you stop at this level of understanding and generously ignore what comes next, which I pointed out for a zillion times about TDS-meters as not qualifying for a standard unit, you indeed miss the crucial point. Because this is the part where the real confusion with standards and units starts and where any recommendations or tables expressed in ppm are just confusing and even useless without a conversion rate. Simply read tthat part again and do not think of it as coming from me or someone that wants too look smarter than anyone, - and you may finally get the real sense and the importance of it! Then you may even deduce from it WHY electrical conductivity is the only valid unit when it comes to measuring and sharing, discussing or whatever in the context of TOTAL CONCENTRATION and anything related to it only.

In case you will actually get to make your own nutrients and eventually make them up, you will perhaps realise what the point of confusion about single elemental and total ppm of a formula, versus EC/ppm with actual measuring of total concentrations of nutrient solution is about.

Btw; Anyone who makes their own nutrients with a nutrient calculator can actually tell how many ppm of each single element are present in a specific concentration they make up - because the formula of the nutrient solution is an actual KNOWN, at least for a fresh nutrient solution.

You remind me the Zen disciple who declared: "I drank all the Tea in China and yet I am not awakened!?!" ;-)

lucas_formulas
I get that you dramatically recommend using EC rather than PPM or TDS. That's fine, but that is your debate not mine that you claim there is no need for. Everyone should just do what you say instead of what works for them, as usual. You still have not shown/explained that EC can tell you anything other than a "RELATIVE" nutrient concentration. I understand that you feel it's more accurate, but it still cant do anything else.

Sure anyone can figure out the exact PPM of each element in a fresh batch of nutrients if they really wanted to. But who changes there nutrient solution every day? Most people think that just by getting the numbers rght on the meter, means that they have the perfect nutrient solution, weeks and sometimes even months later. But plants don't absorb nutrients evenly. So over time, that's useless for anything other than saying the solution has gotten stronger or weaker. The "RELATIVE" nutrient concentration.

RELATIVE
Because it's not exact as to what elements are actually in it, not even close (no mater what meter one chooses to use).

And in fact the relative part is what allows people to grow effectively using PPM, they just can't communicate any nutrient information effectively.

I'm switching to an ICP mass-spec to monitor my solutions :)

@ zathras
The relative part (single elemental data) using ppm as a unit, can only be communicated between people who are able to understand ppm data in a nutrient formula. These are mostly people who have experience with composing and manufacturing their own nutrients from salts and raw materials. They can communicate this information very effectively indeed, simply by exchanging formulas with all necessary data. Indeed data that both sides can read (even interpret) and translate to a nutrient solution. But anyone using a ppm-meter to measure total concentration of any NS has to be aware that their instrument transfers (actually computes data) to ppm from original electrical conductivity (EC) reading using a specific coefficient or conversion rate. If they know so- and also communicate that conversion rate in annexe to the ppm data, they can at least communicate total concentration "effectively". But if any side ignores that fact, it is a 50/50 chance they would NOT EVEN communicate this basic information "effectively" ;-) THAT is what makes tables and ppm recommendations without telling the conversion rate USELESS. If using EC as a unit, at least this part is unambiguous.

Quote zathras:
"I'm switching to an ICP mass-spec to monitor my solutions :)"

Ha -Even then, you can only analyse samples, not even monitor your solution in realtime. And for the "communication part" it will be rather unilateral or not be satisfying. You would proudly tell others what you have got, and the feedback to it would only consist in pure envy LOL!

"The relative part (single elemental data) using ppm as a unit, can only be communicated between people who are able to understand ppm data in a nutrient formula."

It is not a mater of understanding the ppm data, it is a mater of measuring it. If you know exactly what you put in it (when it's fresh) then it's not a problem. If you are using a commercially manufactured nutrient, then you may be able to figure it out (when it's fresh). But weather you manufacture them yourself or use a commercial nutrient there is no TDS, PPM or even EC that can measure them and brake it down accurately after that (or even then). That's why they are all just a relative measurement regardless. I can give lucas that all the meters start from electrical conductivity, they are electronic devices after all. But that does not change the fact that none of them can tell you exactly what is in a solution, just give a total reading.

Lets say there was a meter that did break it down into individual elements, that would be great, right? Most manufactured nutrient solutions are a 1,2 or 3 part nutrient solution's (and are what 90% of most growers use). How does it help to know a solution is lacking, lets say Magnesium? Not much because unless you can just add the lacking Magnesium (not possible with pre-manufactured nutrients), then it's kind of pointless. You will still need to change the solution in order to maintain a balanced nutrient solution.

zathras
I'm interested in the 'ICP mass-spec" that you mentioned. I have never herd of it, sounds expensive. Do you have any links to what you are referring to, I'd like the check it out even if it is expensive?

Forget the ICP - it was a joke. It stands for Inductively Coupled Plasma Mass Spectrometry. It's used for doing trace metals analysis in laboratories. But if you're really interested, below is a link to some used ones. And you can probably get by with just a plain old ICP and do without the mass spectrometer part.

BTW, there is also the older metals analysis technology of Flame or Graphite Furnace Atomic Absorption Spectrometry. The difference between the technologies is pretty much how the metals are converted to vapor for the actual analysis. There are also differences in the levels the different types of devices can detect, flame the least sensitive to ICP MS the most.

Certainly it would be absolutely irrational and expensive to run your own mass spectrometer at home, lol.

However some of you might be interested in knowing that I have achieved good success in monitoring K, Ca, N (as nitrate) and N (as ammonium) using an ion selective electrode array. I am still working on this but I have been able to monitor the change in concentration of individual ionic species with good accuracy (comparing my reading to samples analyzed using atomic emission). Other elements have been a little more complex, particularly P due to the changes in species with pH.

However it is possible and it can be done with the adequate equipment. It is not cheap and it requires extensive calibration but it works and you can actually see how your plants absorb certain ions independently 24/7 :o).

Just wanted to let you know this indeed can be done !

Daniel

zathras
Thanks for the explanation, I take it, it's used for trace metals. So I guess it wouldn't really work on dissolved salts, unless they were metals. I was just curious in how it worked. But that does look way to expensive to consider any time soon.

danielfp
Thanks for letting us know about the "ion selective electrode array" your working on. Even though I doubt I would be able to afford anything like that, I am always interested in the technology, how well it works and how accurate it is.

The ISE's are indeed a viable option. They are certainly a pain to calibrate and maintain, but do provide real-time measurements. And actually, they aren't that expensive. For a couple of thousand or less (even Amazon sells ISE's) you can configure a decent system. The metals are probably the least important to monitor.

Daniel, what are you growing and what uptake rates have you seen for the various ions? I'd love to see any data you've accumulated!

Hanna makes some interesting multimeters. They aren't real time, but cover all the nutrients at a very reasonable price and would be a lot easier to use than ISE's.

Hello Zathras,

I have been experimenting mainly with basil, parsley and tomatoes and I have been particularly interested in the measurement of nutrient uptake as a function light source (natural, LEDs, HPS, etc).

The results have definitely been interesting and my conclusions right now pretty much agree with previous published studies with ISEs on the field. For example I have observed very high intake of K+ by tomatoes with a moderate absorption of N and a not very large absorption of Ca(2+). Of course, the results are extremely interesting and show the complexity and dynamics of actual nutrient absorption.

However even though you might be able to get ISEs for a moderate price you still need an adequate potentiometer and adequate lab equipment to do the calibrations, something that will probably make the setup not worth doing for most people. However commercial facilities would get a great benefit with a small comparative cost.

Thanks a lot for your interest in my work !

Best Regards,

Daniel

I'll keep an eye out for some graphs on your blog ;)

I think I'll try one of the Hanna photometers. The system seems to be surprisingly well designed for consumer use.