hey there Mbatista, measuring EC of runoff from soil medium is totally useless as you can see from your readings. You're doing everything correctly but the problem is the EC/PPM meter measures particles and their conductivity right? so there's plenty of soil particles that are minerals in the run off so you're measuring (also) that more than you're measuring actually the run off from your input. It's an interesting experiment to make, but it doesnt tell you anything about the runoff you're interested in. That's one of the disadvantages of soil ! your grow looks perfect , just a tiny bit overwatered... Hope this helps ! π