If the cause was actually too much light, which would be very unusual and difficult to accomplish, then yes they will recover. But the odds strongly favor some other cause than the lights, especially with 14" spacing from the plants and the standard # hours of 14-16 on. Exposure to light, unless excess trapped heat and stagnant air accompanies it, poses little threat. If heat and air circulation is the issue then increasing the air circulation among the plants with a small fan solves the problem.

Far more likely causes of yellowing is overly wet soil which causes root suffocation and root rot. It is caused either from over-watering or poorly draining media and containers.

Another possible, but not as common a cause is lack of sufficient nutrients. What and how much have you fed the plants? What nutrients do they have available?

Dave

Hi Dave,

Since the problem started as soon as the plants emerged I think call rule out nutrients or root rot, heat however may be the problem. I've fed them since the primary leave emerged with Maxigro diluted according ti the directions. I'm not totally for certain yet but I think cutting back the duration of the lighting is making a difference. As always I will soon be putting a fan on them to help stimulate the stem resiliency.

Thanks very much for your help.

I too find it unusual for it to be lighting. Heat, maybe. Put your hand under the lights, are you feeling heat? Get some fans going to help with that. 8 hours is not very long to have lights on the plant, you should be aiming for more hours than that. Additionally, I checked out the link you provided. The system comes with T5 bulbs, which will run a little warmer than T8's but would no way burn seedlings. I really don't see a light problem causing your issues, I agree with digdirt2 above, either overwatering/drainage issues and/or fert issues. Maybe too much fertilizer is compounded by a wet medium. Any way to post a pic?