Browning leaf tips and yellowing leaves

As the title suggest, my 2 week olds are browning and yellowing, under a 400w HPS about 1 and a half feet above. Haven't fet nutes and only water every 4-5 days. Have them in 4 gallon buckets and on a 18/6 schedule.

Any ideas?

pics would help. What is your medium and what amendments did you add. Did you recently transplant into the pots they are in now? Sounds like your mix may be a bit hot.

Drink!