Athosanswered grow question 6 years ago In order of priority. First temperature, for lights on 21ยฐC (70ยฐF) is low, you need to get it above 23ยฐC (73ยฐF), with the right temperatures the plant will explode with growth. For lights out 15ยฐC (59ยฐF) is too low, try to keep ir above 20ยฐC (68ยฐF); 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.