Cannabis, and many other plants get the majority of their nutrients from the top 4 inches of soil. The mcrolife will migrate down into the soil and the nutrients will leach in also. I grew an Auto Ultimate in a 20 gallon SIP, in organic soil. I topped dressed twice. I scrogged the plant and pulled 312 grams dry from her. And nothing says you can water a SIP from the top occassionally. Stop the bottom feed for a couple days, dress and water from the top. Resume bottom water in 2-3 days.
Cannabis root structure, even in a pot, there will be more roots in the top layer, even when root bound!
View attachment 1225586