400w grolux too strong?

I have 4 plants under a 400 w grolux sodium light. I had the light about 12" from the plants. They went well until they reached about 2" high but then stayed at that and started to whither. I then moved the light up to about three feet away which did the trick and they started growing like mad and looked really healthy. Now they've got to about 4" high but have stopped growing again and look a bit droopy again. Is this bulb too strong????

Your light should be no less than 3 ft above the tops. But need more info! room size? what kind of food? Are using a fan? how often do you feed? 400 watt HPS is enough for 4 plants But I think 3 plants would be better.

as they get bigger they will need bigger pots , and also they will consume more water. so you might be underwatering. Or they might be root bound

are these new seedlings

My guess is that it's getting too hot. If you can attach and inline fan it would be best, but an oscillating fan would help a ton if you don't have one.