burnt tips

it's my second grow and about 35 days old...yesterday I changed the light...the weather was a little hot about a couple of weeks ago but now it's alright... the tip of the leaves slowly turning light green and the yellow and burn... I noticed it about a week ago... now it's still going...

I have ????s on why the tips are burnt on this individual plant. Is it the CFL (23w, 2700k, 1500 Lumens) I installed? Its about 2-2 1/2 inches from the plant. The plant is 3 weeks old still in Veg. stage. I have it (and 7 others) in MG soil, in 8oz red beer cups. Not sure of the Ph or temp but...

First time grower here, At first I heard from the forum that I had over fed my plant, and that the yellowing of the bottom fan leaves and burnt crispy brown tips were a result of too much Nutrient build up or a lock out. I flushed her with 700 MLS water, I've been leaching her as much as I can...