you can't really overwater rockwool because the water drains from it. your 10% run off is correct and im sure @tobh can explain better than i do but don't over think it too much.it measures 2.7 in the 2.7 solution. maybe my understanding of rockwool isnt correct or im overthinking it myself . by the last watering i should have 10% runoff correct?? i dont know where i heard that but it sounded right to me and i figured it would be a start. that's what i based my volumes on really once i moved them into the 4" cubes. my understanding of it may be leading to excess dry backs causing tension in media and high ec runoff. when i upped the volumes it wasnt enough and pushed everything to bottom of cube is my guess. man what a ride!!! but its enjoyable to say the least . im going to figure out if you can overwater rockwool today and ill let you know lol!!
Just let it drain until the reading is the same as going in.