Are you using Coco Loco or Cultivation Nation?
Their Coco Loco mix is: Aged forest products, coco coir, perlite, earthworm castings, fossilized bat guano, Norwegian kelp meal, oyster shell and dolomite lime.
This is why the package tells you to treat it like soil except water less frequently.
Get an EC pen and measure your feed. If you want to go with drybacks, you can do still do that (if you're in Coco Loco), but feed with nutrients every single time you water and feed at around 1.0-1.2 EC to start.
At 9 weeks in, you should be stressing out about running out of room and how you're going to manage the stretch in flower. Those little shits need some nutrients.
While you're at it, what is the light, the dim setting, the distance, and RH/temp?