dying patches in middle of leaf????

Howdy all green fingered people.
Anyone have any idea what this could be?
growing AK48 under 400W HPS (organic in soil) 4th week into flowering, and all was good. then I noticed these dying spots in the middle to end of the leaf starting with the older fan leaves????? see pics
Generaly the plant is very healthy and the greenest I have grown.
I have read and re read the FAQ and still haven't got a clue what sort of problem it is???
any advice would be very welcome.
Many thanks from Afro the DnB clown.

Take some pics when the hps is off or fix the white balance so we get a true look at her colors.

It could be nothing just the plant begining to eat the leaves fpr flower. Could also be a slight ph issue. I would not be to worried. Flush and continue. She looks good.

Thanks lefty.
I will take more pics when light goes out. Not too worried but want them buds as big as they can get.
peace from Afro the clown.

look at trhe underside of the leaves, check for bugs