Hey ppm or ec is only important when you feed mineral nutrients,if you feed organic nutrients ec or ppm is not important because there is none in organic nutrients,you feed the microbial and bacterial life in your soil so they can feed your plant
Ec or ppm is only used with mineral nutrients
You measure the electrical conductivity of the water..the more minerals and salts,the higher the ppm or ec..
An 0.4 ec or in ppm 250
Is a great ppm or ec to start with,your ec reading will be pretty spot on..
My tabwater is at ec 0.9
The only thing here is when you mix in nutrients tot let’s say ec 1.2 you have .8 ec nutrients
So I have to go to a ec of 1.7 to get to the same nutrients level as your tabwater