Why do plant leaves turn yellow?
I know that sometimes, either watered too much or too little and over fertilization or too much nitrogen...anything else?
They are just getting them on their tips of the leaves?!?

not enough nitrogen also

got any photo's? get a ph kit.. what kinda and amounts of nutes you using?

Lots of reasons for leaf tips to turn yellow, not the least of which is lack of nitrogen like draig says. Also, heat will do it, so where are your lights? Mites will do it, lots of things will do it and sometimes you just have to sort of troubleshoot your plants by trying various things, but not so much you ruin your babies. Could be lack of O2, just loads of reasons why. PH is a pisser also.

Get a kkit from True Value Hardware that has the N-P-K and Ph test in it (2 tests for $5)
If you run the tests, and they are ok-- then look at how far away your lights are-- or mineral deficiency...
how often/how much do you water??

the lights that we have are HID 400 watters and the type of seeds are purple #1 feminized by Dutch Passion. I will certainly try the ph tester, and they get watered as soon as the dirt is dry to the touch, pretty much...

TIP YELLOWING OR BURNING IS MOST OFTEN CAUSED BY NUTRIENT STRENGTH BEING TO HIGH OR NOT FLUSHING WITH FRESH PH BALANCED WATER OFTEN ENOUGH, LACK OF NITROGEN WILL NORMALLY RESULT IN YELLOWING OF THE LEAF ALL OVER & MAINLY ON THE LOWER LEAVES WHICH OFTEN HAPPENS TOWARDS THE END OF FLOWERING WHEN NITROGEN IS TAKEN FROM THE LOWER PART OF THE PLANT & USED ELSE WHERE AS NITROGEN IS A HIGHLY MOBILE ELEMENT, DO STILL CHECK PH LEVELS TO MAKE SURE NOTHING IS BEING LOCKED OUT......

Please turn off the caps!! It hurts my eyes!