My first dwc grow mixed genetics

This is my first run doing a 4 site non recirculating dwc. As soon as they sprout up I mist them with a low concentration of rhizotonic. I will be using the full canna aqua line including all the additives, plus some cal mag. All water used is reverse osmosis ph to 5.8 18/6 light cycle for veg 12/12 for flower. I am running 2 autos and 2 photos this grow. Day 3: all of them seem to be stretching too quickly. I adjusted the lights closer to combat this. Spraying a couple times a day with a 1L spray bottle with 2ml of Rhizotonic. They are being grown in a humidity dome. The temps have been around 72F-75F during the day and sometimes dipping to 63F during the night. We are currently experiencing severe cold weather in the area and my heat pump is struggling to heat the house. The humidity in the tent today was low, around 38%. I have a proper dehumidifier however, I haven't had to battle low humidity in the year Ive been growing like this. I have a small humidifier that can hopefully keep up.