EC of 8 starting out (from RO Hydrologic Stealth 150. Do I add the goal EC (2.1 per Athena Instructions) to the 8 I started with?

The ec coming out of your medium is 8us/cm ? Are all terms used in water quality measurement to describe the concentration of dissolved solids in water. Measuring ec in and out is done with a TDS metre. This measures total dissolved solids (not actual salt ions) so it doesn't actually give accurate readings of the electrical conductivity of a solution. It tells you everything that's "not" water. 99% of guides will tell you to measure the solution In and solution out. With enough knowledge you can determine what's going on inside the medium. But in reality you are not really accurately reading the electrical conductivity of the medium, your guessing based on how much tds was in the water. This method works so well when you use synthetic fertilizers, everything is fed based on it being readily available right there and then. Once you start to use slow release organic fertilizers it drastically changes things up. Growing becomes far more about what's actually happening in the medium with accurate ec readings using a ec metre designed for soil. Upto date accurate readings that remove 99% of all guesswork. Ec is low? Watering time, Ec still low? Fert time. Everything is super simplified. For me at least. but I don't grow using conventional methods taught through online guides. Ec is the salt capacity. 0.3-1.8 Cec is cation exchange capacity of a soil. Most people who grow using synthetic have very low cec. If you run a very high cec. Dramatically alters how you need to monitor your grow and its medium ec. You can't just read what goes in and goes out when 90% of the CEC is in the soil and not the solution. You need to know what's going on inside. Ph determines the electrical balance between + and - of that salt capacity. Your job is to keep everything 50% + and 50% - Ph of 7 = 100% of available cation sites in medium are filled with one of the following key cations include potassium (K+), calcium (Ca2+), magnesium (Mg2+), and ammonium (NH4+), among others. If your ph is 6 then you need to add more of those to bring back the balance towards 6.8-7.

Very unlikely it is an 8 EC. The callibration is off or it's a 10^-1 situation on the readout for some reason. For ssmoe reason not in "millisiemens." So, re-callibrate your device and re-measure. If it reads 8 again, get the device manual out and look for anything odd about the scale it is using. Probably a .8 at that point or defective equipment / dirty probe. 8ec would absolutely kill the plant, lol. You wouldn't want a 2.1 the first week anyway, so the instructive videos may not be as useful as first thought. Seedlings power themselves, so better to take your time building up nutrient concentration in medium. Nutes that require bacteria and other microbes to break ignredients down before they can physically enter the plant read at a higher EC than other options. 2.1 is somewhat exaggerated relative to what the plant has access to. Even so, 2.1 would be high for a seedling stage plant. your first grow i'd take notes as you go and err on conservative side to start. Never let it get unhealthy, but you'll better understand the edge you want to ride. With your notes, come up with a plant to ramp up faster or slower based on what you saw... or to level off higher or lower than you were instructed. Try not to waffle on what you do or it is harder to make adjustments for a future plan and a better plant next time. LOL i'm talking about soil.. "hydro logic?" so if this is hydro or soilless, fertilizers used should be 100% plant-ready and 100% soluble. Not counting your tap water, should probably be up near 1.3-1.5EC (mature plant, not seedling) If you have hard water, you might surpass 2 EC, but it'd have to be pretty hard tap water to the point it might start interfering with fertilization... borderline. i'd stick to ~1EC for seedlings, based on 500-scale conversion. 500-600ppm is enough and easy to ramp up to ~750ppm withough a huge shift occuring all at once. EC doesn't convert very well to elemental ppm. For a resolved understanding of the nutrient ratio, need to calculate ppms from the labels. there are free apps that do the work for you. Or, could become familiar with weighted-average by-dose percent of mass values - again off of labels. if a fertilizer has 10% Ca, but only 1/10th of the total dose (mL or grams etc per volume), it's 1% Ca --- plus any other ca added would add to that, weighted by portion of dose. you basically do a weighted average N/P/K and secondaries based on your dosage. == ratio of nutes and your EC informs about overall concentration. mission accomplished, too. With either, over time you'll see upper/lower thresholds you want to avoid or maintain based on expected health of the plant. What you can exactly feed depends on far too many variables to be the same as the next garden.. the more tightly you control climate or addition of co2, the more you can feed without toxicities building up.

EC ? forget it we're using NPK ppm so that we can adjast the growing needs for 1 week u'd using 150-250ppm 2 - 250-350 ppm etc EC could be 0.5,0.65,07 so ur 2.1EC with 0.5 ratio would be around 1k ppm that shurely kill the plant