TDS and EC are, essentially, different units of the same measurement. TDS is total dissolved salts. EC is electro conductivity (i believe) which is the amount of current that a liquid can transfer. The conductivity of a liquid is directly related to the amount of dissolved salts in the solution. So basically you should be able to work with what you've got. do a google and I'm sure you'll be able to find a conversion for them.

Hi Satcat, My quick answer to your salimeter question is that I doubt that you will be able to read the concentration of a hydroponic nutrient solution with it, because the nutrient solution would be far too weak to give a reading. Many years ago I gave up using a conductivity meter because I could not correlate its readings with what I knew was in the nutrient solution. So I ditched the conductivity meter. However, I would advise you to get a good pH meter and know how to calibrate it properly. I explain all of this on my Australian web site below. If you save each page of my web site, as its own name, on to your computer, all in the one directory, then you will be able to navigate from page to page with ease when you are off-line. Go to the page "Hints for Success" and read Tips number 4, 5 and 6. Tip # 9 is also worth reading. See also my "FAQ" page and see what it says about "osmosis" and making your nutrients too strong. If you have any queries, just use the email address on the web site. Cheers, Jimr007 Australia. Here is a link that might be useful: Simple Sand Hydroponics

Am I truly the only person here who can see the REAL paradox with buying a so called TDS-meter that converts to a "fictional" ppm content of the actual nutrient? While a more common conversion rate of 1.0 mS/cm to 500 ppm is some 15-20% off the actual ppm content of a common nutrient solution, a conversion rate of 1:700 is just completely off the real thing. First of all the information "capsicum ppm should be 1260-1540" is just an abstract, without giving either the conversion rate- 500/700 or stating that it is the amount of actual elemental ppm, which indeed is a very different thing on top of it. You should always using (well I believe that's what everyone is aiming for) the proper and balanced amount of nutrients, not some non-defined number that varies with conversation rate, right? Imagine farmers in Western Europe, the Ukraine and India, using different weight units. While the Europeans have 1000 milligram per gram, the Ukrainians' unit, when converted is only 700 milligram per gram, the Indians use a unit that converts as little as 500 milligram per gram. Now there will be a worldwide recommendation for the use of Nitrogen for peppers that says 10 gram per square foot. So, will the Europeans be the wasteful, the Ukrainians perhaps getting it right and the Indians saving millions? Nahhh.... Simply take your tap water, you say IT IS ABOUT 420ppm. Well IT IS NOT, only your instrument measures and says falsely 420ppm. Get a official or lab analyses of the same water and it will, as sure as I sit on my bottom right now, NOT tell 420 ppm. Measure it with a Hanna conversion rate it would be only 300, - but how much "dissolved solids in ppm" has it for real, how much ppm are there actually in that tap water?! The truth is that neither a EC-meter, nor a 500 conversion or a 700 ppm conversion instrument can measure it. Only a dehydration can tell the total dissolved solids, and only a analyses can tell how much ppm of each component there is. The very same thing applies to your or any other nutrient solution. As long as we don't talk (and actually measure) EC and mS/cm for a nutrient solution, and use PPM ONLY for the elemental/actual content of each of the Macro- and Micro nutrients (as in N= 150ppm, P= 35ppm), - there will always be confusion and ERROR!

Basically, what hex says, and just to add that a 342 calibration is a weak solution and more suited for testing most tap water. But such hair-splitting accuracy won't play a roll in your hydro need as long as you have a way of telling stronger from weaker on any calibration at all. The actual calculations the stick is giving are really a black box if you start splitting hairs and ... conversions get hairy when you deal with summer vs. winter on top of who's calibrating with what and at how strong and at what temperature. Sticking with EC frees you from ever worrying about ppm conversion factors again, except when helping others wade through the mess ppm has caused. So, you can complicate life with ppms or just use the actual signal of the stick gives, which is EC, and never look back, because the ppm is not what is being measured, it's the EC. The only benefit I see to "ppm meters" is that they are cheaper, but not by much. If you wonder how something that has programmed into it an extra level of conversions can be cheaper that the one that simply gives the raw electrical number, it's because mass produced meters are TDS since tap water is usually measured in ppm, and the guy that started making EC meters makes them in smaller runs. In hydro, there's a case to be made for those using a single brand of powdered fertilizer that ppm is easier to relate to gram readings, but to be honest I have never once seen a single post of someone actually using it for that. If you add up the ppms we are actually interested in, like N, P, K, S, Mg, Ca, Fe, etc., the total won't add up to the ppm on your meter, so why bother? Since you already bought TDS, consider it like a speedometer. Mix the ferts new, and check the reading. The reading is your rough speed limit. No one will give you a ticket for going a little bit faster or slower, but major differences and your plants will need to pull over into the shoulder. If you use EC, though as already noted, you will be able to share your results without everyone degenerating into a ppm vs. EC food-fight! EDIT: Let me add, for your purposes, it is not the NaCl calibration with 342 ppm NaCl that will make a squirrel's ass difference. What you want to make sure is that it is compensated for temperature. A 342 ppm calibration would be extremely inconvenient for me if it were only done at 25 C, and not automatically compensating for temperature ("ATC"). Many of the cheap meters do not have ATC, so watch out since even one degree make a difference in solution measurement. for a typical 10 C temp dif, the uncompensated readings of the same brew will be 20% different - and that becomes a problem! This post was edited by PupillaCharites on Fri, Apr 4, 14 at 15:56