Nutrient measurement

TDS pens measure EC and convert to ppm using a simple factor. Depending on the brand of the equipment it may convert to different PPM numbres... So, use EC for the least possible miscommunication. Most products in north america are on the "500" scale.. so 1.5 EC is 750ppm on those brands, but may be different with another brand. Whne irrigating or fertilizing, always ensure entire pot gets wet... usually a minor amount of runoff is necessary, but if you pay attention over time and consistently water at same pot-weight, you can dial it in pretty damn well. soil ec... slurry? slurries and runoff is not a perfect indicator of the substrate... it can be useful info to track.. make sure you measure at same points of runoff or use same volume of soil and same volume of water of a known pH before you mix it up and measure. it'll always be a bit off from what the soil actually is, but over time you will learn normal range and how to react if it exits that happy zone. 1.3-1.5 is what hydro/soilless typically uses. (slight increase between irrigation in soilless with a little evaporation occuring) In soil you likely see it spike higher then drop back down as you alternate in some patter with water and fertilized water.. whatever that pattern may be.. every other? every third? "on demand" will typically work out better so, more fertigations with slightly lower concetrations are probably better than gassing it one time, then feeding water for a couple gos. and that's where your testing over time can help you dial it in... you want to find a dose and frequency that maintains a certain aamount of nutes... neither dropping or rising over time. it may need to be higher in soil with soil nutes... if oyu have to rely on bacteria fixating or chelating molecules in order for the plant to uptake them and use them, even though that stuff cannot fit into roots in original form, it still increases conductivity of the liquid it is dissolved into.... so yu get higher EC but as far as what enters the plant is lower. (otherwise it's evaporation-caused spike or simply feeding too high of one.)