I read your article; very informative. I would like to point out, however, that all most growers need is a "benchmark". By that, I mean something akin to a "home plate", a starting point that remains in the same place (constant). I use a Bluelab Truncheon. It has little red blinking lights (LED's) and it gives me a "base-line" from which to maintain some consistency in my nutrient solution. It's a no-brainer to use; very simple, rugged and accurate tool! I brew my own nutrient and the water I use is loaded with calcium; having an EC of 1.2 right out of the tap. If I didn't have a way to measure that, I'd miss my proper EC range by a mile, so for me (and most others) a consistent tool is a necessity. Granted, the Bluelab Truncheon is the "Gold Standard" in our industry and even though it was a little pricey, I have no regrets. It's trustworthy (I know, because I test it against a "known" every now and then). Your comment regarding EC and pH is a very important point. Depending on what one uses as a pH up or pH down, the conductivity can become somewhat of a joke. My nutrient is self-buffering, so I adjust its pH in a totally different manner (Lewis-Bronsted Acid-Base Theory) than the rest of the crew here on the forum. Still, I always test EC before, during and after brewing a batch of nutrient. It's THAT important, to be sure! I have found out (the hard way!) that growing stuff outside the accepted standard EC or pH range can be disastrous. I post links to EC and pH range charts on my Web page. There really is something this "EC" business.

I bought this one. It was about $55 after s+h. It's quite cheap relative to others, and comes with batteries, but it's not clear how I'll be able to change them out when they die, since it seems to be a solid unit. Here's a picture. Oh well, I'm sure it will last a few years anyway.

Would like to add and correct a few things here: 1. Pure water without any dissolved solids does conduct electricity pretty well, (try to put 110 or 220 volt in recipient with 100% pure and distilled water and put your hand in there!) the difference is that, the more dissolved solids that are dissolved in the water, the higher the conductance of the water. 2. Lots of talk has been done about PPM conversion rates that are based on electrical conductivity EC reading of mS/cm but converted to various PPM rates, mainly 500 or 700. Do they correspond to actual PPM of any nutrient solution, or not, are they related directly or not, how comes etc. I guess many people haven't understood why and how it is. It's simple: The actual ppm value of a specific sodium chloride solution is very close to half of its conductivity value (in microSiemens/cm), That is why these "TDS" meters display the conductivity as an equivalent NaCl amount (1000/2= 500). The 700 conversion rate is derived from a specific potassium chloride (KCl) solution instead. Important: both ppm readings of either conversions used here are not related directly to YOUR or ANY nutrient solution or their actual and total PPM content in all elements. Hence, never think that a ppm reading of any TDS meter expresses any actual ppm of your formula or solution nor can be compared to any ppm recommendations for single elements as in N= 180 ppm, or P= 250 ppm etc. BUT it happens that the reading of a 500 conversion rate TDS-meter is quite close to most nutrient solutions, generally the reading is 10-25% higher as the actual content in ppm. It varies with components used as in the actual composition of the nutrients. Fortunately or unfortunately, however - do not confuse the ppm reading of any TDS meter with the exact content in ppm of elements in your nutrients or the total dissolved solids it contains. 3. As for the use of ppm readings and data (of a so called TDS meters), you may pretty well state ppm readings and data in forums as long as you know and TELL the conversion rate that goes with it as well.

I tend to think and express in a pragmatical way, without loosing "the facts". And what matters to me is what is truly applicable in any context. @ mikey_2 An EC-meter measures electrical conductivity based on total ion concentration in water, that's right but it doesn't tell you the ion concentration, nor does it translate it in numbers. Form a EC reading you can't draw any conclusion unless the ingredients that give a certain ion concentration when dissolved in water, are all known. Single components have a known conductivity in relation to ions and ppm they leave when dissolved in water. But different components as part of a nutrient have various and hence relative conductivity factors. Thus the EC-reading can't give you any information about ions or ppm present, neiher of single elemental, nor of total ppm. Only If all components and their parts are known, EC-reading in combination with this info can give you total or individual ppm content only. @ joe.jr317, Does any unit, ranging from foot, over kilo to gallon have got any "meaning" without cultural components and connotation? They all haven't got any meaning unless we "made it up" and got used to them - and yet they all serve us pretty well. Even the metric system based on Earth's circumference has a solid geometric base (indeed) but does that mean anything practical in daily use, or does it help US people to adopt it? ;-) With so called TDS-meters (and the fact that they use ppm as a unit) it's different. Here we deal with a clear discrepancy, when using this "unit" with a nutrient solution. Because here the use of this unit creates the illusion we deal with something precise and known when we don't. It doesn't only create the illusion of a known unit, but there are 2-3 conversion rates in use which is causing even more confusion. As I explained earlier TDS meters translate in either NaCl or PCl standard, and thus have strictly NO correlation with the ions or ppm present in any common nutrient solution. To be even more clear: when using any of these so called TDS-meters of any conversion rate with a nutrient solution, it gives a FALSE ppm reading. And that's the important point and difference here, I believe. So my conclusion simply is to stick with EC, as at least it gives us a unique and true unit to get used to "culturally" and allows us to reliably use and work with. Furthermore, from EC alone we can draw conclusion of actual PPM content in a nutrient solution, as soon as we know the ingredients and their part. PS: The fact that a nutrient solution changes with plant's uptake and that measuring it's concentration gets more and more unreliable because of the + and -ions changing, doesn't affect the choice between a EC or TDS-meter or the respective preferability of a unit. Both instruments are equally concerned by this effect. And as we are at it, with a more advanced monitoring of both, PH and EC changes we can indeed draw conclusions to improve concentration and composition of a nutrient with the goal of keeping the balance as long as possible instead of changing the nutrients "frequently". Hence If in the right hands, a EC-meter (in combination with a PH-meter) becomes more than just a maintenance tool. ;-) Cheers and we are in peace - always, Lucas