Fastbuds autoflowers in autopots

Ran out of soil and thinking of running coco next grow so I just bought a bag to add to the top. I figured why not? Plus I think it won't attract gnats as much. I think the light at 24 inches stressed a couple of plants even though I had the wattage turned down and stacked one of the six shooters too much with my LST that later stunted 2 of my plants which 1 was thrown out