Plant is yellowing dont know how to fix it

hey guys i have some nice buds forming but for some reason the leaves are yellowing....I thought it was maybe heat but its at a constant about 75 in my room. then maybe nute burn but I have been just watering and it is still turning yellon on the tips and a little on the edges?????

I can't tell from the pics but are those the lower fan leaves?

Most of the time the lower leaves will die off to give way to the upper bud leaves. More of a direct injection of light to help the flowering.

If it is in fact the lower leaves then don't worry about it.

It's still early for the fan leaves to start dying.
From what I can see from the pics, looks like overfert.

here are two very useful links: http://www.icmag.com/ic/showthread.php?t=11688&page=1 http://www.greenmanspage.com/guides/tables.html