Hey there! just curious, how much air do you have in those buckets? What airstones are you using and what is the water level in relation to the bottom of your net pot? I think your plants are growing slowly because the roots probably were not poking out the bottom of your rock well cube when you put it into your bucket. I assume your cube is staying too wet to promote the root to grow and search for water. When we are using any form of DWC buckets you generally want to grow out your seedlings on a cloning tray in their cubes under some low wattage lights. But keep them close to your plants and only water the tray slightly. This will ensure that your roots will begin to stretch out looking for water. so that they begin to poke out the bottom sides of your cube then t that point you put them in your net pots. You want your water level a good 3-4 inches below the bottom of your net pot. So that your air stone bubbles the water aggressively enough, that it is slightly spitting water up at the bottom of your cube.
Other than that, your temp gaps are nice and tight, however, I would raise the temperature up and try to keep it between 79-84 F during Lights on and no less than 9 degrees during Lights off.
Cannabis plants during seedling / early veg phase love heat and humidity it's the buds in flower that hate it.
If you have any questions, just message me and I'll help out as best as possible.
Happy Growing!
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