Please help problem with seedlings

[tadaa]

I have no idea what's causing this but most of my 3 week old seedlings are yellowing, and some leaves are turning black at the tips and crumbling. It's not the soil because I've used it before, and I'm also using 2 different kinds of soil and it's happening in all the pots. However, 1 plant is doing great so that rules out the light being too close. It's a 600watt bulb and out of desperation I've moved it about 2.5 to 3 feet from the plants. I have no idea what is causing this. Any ideas?

[Garden Knowm]

what is your watering schedule?
are you over watering?

:)

[tadaa]

what is your watering schedule?
are you over watering?

:)

If that was the problem I doubt some plants would be doing fine and others dying.

[stone eng]

You did say
most of my 3 week old seedlings are yellowing. If I had to guess I'd say that over watering was likely, either that or some kind of root rot. The only time I've seen black leaf tips are on failed clones. Overwatering either seedlings or clones will cause yellowing, wilting and ultimately dead tissue. I'd have to agree with Garden Knowm, Although I'm far from an expert.

[tadaa]

My point is that some are doing fine. If I was over watering all the plants would be having problems.