Hey guys, compared to other grows in the week 8 s...

In order of priority. First temperature, for lights on 21°C (70°F) is low, you need to get it above 23°C (73°F), with the right temperatures the plant will explode with growth. For lights out 15°C (59°F) is too low, try to keep ir above 20°C (68°F); Second, pH. In coco ir is a must to meassure it and adjust it. You probably have many nutrient lockout due wrong pH. Third, EC/PPM. Again, in coco it is a must to meassure it, in order to feed the right anount of nutes. Fourth, humidity. Just like temperature, with the right RH, the plant will grow real quick, 30% is too low. Your exhaust is probably too strong, tone it down and your temperatures and humidity will go up.