Wedding Cookies II - First Grow

I have all 4 plants potted now and under the mars hydro light. The light is 310 watts, so it's set at 25% brightness. The light schedule is 18/6. 2 of the plants look great, one is slow starting and one looks like it's going to die. I noticed it was a dark green so I am cutting back on the nutrient on it and using straight water I ph balanced to 6.5 and dechlorinated. The pics aren't that great, but they are still pretty small. 2/11- I made a few mistakes on this grow so far. The first is putting my heater in the grow area instead of right outside like I had it. The outside temperature is close to 0 degrees F, so I put the heater in the grow room and cooked 2 of my plants. One dead, the other I am trying to save. Luckily, the other 2 plants are doing good. The second mistake is using coco coir plugs after germination. Instead, I should have planted in the final container. Third, not enough water or nutrient. Today I fed the 2 good plants, then watered until I had runoff. The water coming out of the containers looked like tea so I don't think I am flushing correctly.