First Grow - Classic F1 Auto White Widow

Hope to get some feedback about nutrition : After 1 plant developed a small brown tip, I started feeding. A total of 116.6 liters of water goes into my system. The feeding schedule says that you should give 4 ml of root juice per liter of water. So: 116.6 x 4 = 466 in total for week 1. So, 466/7 = 66.5 ml per day. Despite this, the differences in root growth per container seem very different. 1 bin was so far behind that I changed them. However, after 1 day a brown mass developed in the roots. The others are still nice and white. Is this already the bereft root rot? I've made some pictures and a video. The first plant in the video was first in the container of the third plant in the video. EC value = 0.6 PH = 6.6 Update 3-5 : After adding more air, problem solved. Need to keep an eye on plant #3. I've put sticks on top of the startblock. 1 stick is plant #1 etc. Plant 3 is behind the rest. Root development also differs from the rest. Instead of a long (about 50 cm) long carrot, they are a few short (10/15 cm). The plant is also significantly smaller than the rest. Can't do much now so, let's hope and see she can catch up.