Why Are Some Leaves Brown?

I was just wandering, if anybody could tell me why the tip of some of the leaves are brown. I have herd that it is nutrient burn, is that what it could be? This picture was snapped at week 2 of flowering, it is now week 4 and the tips have not got worse or better. I was just wandering what this is or what it means, anybody know?

too much fertilizer can cause it. Letting the soil dry out too much can cause it. Overwatering can cause it.

I am using the foxfarm nutrients exactly how it says to, and i normally water it about once every 3 days or so. Think maybe I should put a little bit less of the nutrients that it suggests? Or will it be okay, the tip of the leaves are barely brown, and its not getting worse.