HELP.... Plants leaves is discoloring.

Most of my plants leaves got brown tips and only the brown tips are dying. Its still growing about an inch a day. Its already one and half month old and its hight is about 12 to 14 inches. I am using total of 500w light power which is only 12 inches away from the plants, also using two 20w plants bulbs on side. I am using 20-20-20 to water it every other day and spray at least 2 or 3 times a day. Also... I keep it on 16 hours lights and 8 hours total darkness. I already flush it with water once but havent checked the ph level. Could this be a sign of infection or is it normal or what? Its still producing new leaves but within a week or two... the tips start to turn brown and then it look like the tip is dead. Any idea?

Fert max out. The very tips of each leaflette will go a brownish white when the plant is just bursting with nutrients, don't increase on your fertilizer and watch for signs of over fertilization.

Do the tips look like the tips in this pic?

Yes. Also... some of the tips are really big. Few of them is taking half of the leave.

you might be watering to much how big of pot are they in?

i'm wondering what kind of lights you are using? some put off more heat than others...