Can any1 help me?? I have yellow leaves!!

i am still in the vegging process, & a few of my plants leaves are turning yellow, some have brown spots, & others have dead tips..
WHAT AM I DOING WRONG??

how often are you watering? how high is your ph or how low? soil or hydro? temp. in your room? what size light?

watering 3x's a day, PH level is at 5.7 but it was @ 7.1 last wk.. hydro.. room temp is 70 -80deg.. & i am using one 600watt light..

may be nitrogen defficiency, check your ec/ppm levels.

with out pics its hard to say.sounds like nitregon dif. to me also, but then again you say brown spots so that could be too much nutes. check the grow fax under plant asuse, then go to the plant abuse chart.find the pic that looks like your and go from there. if you can't get any picsup for us to look at.