which >slow growth heat or water (coco) ??help

hello temp: 82-84 constant medium: coco light: 400mh, 2.5ft away ventilation: 2fans story: i have 4plants, in 2 gallon coco, 3 weeks (old from sprout), no nute, and plant very small, i thought one was rootbound so i replanted from .5gallon to 2gallon, still showing no progress. first two weeks i watered 2times a day, now i water 1time a day. so question is what is causing slow growth?

1Pic of 2.5wk from sprout blue cheese (2.5in diameter leaf span)

water less, once every 2-3 days. bring lights closer -1-2 ft away. start nutes slowly now. Tried to keep the english simple. Good luck.

thank u for advice