Couple funny looking leaves

I got a few girls going and 1 of the plants has started getting a cpl funny looking leaves. It's not starting in any particular place, just random over the plant. None of the other plants in same tray and res. are showing anything, all are from clones cut from same mother. They're in the 5th wk of flower on a 7 wk strain.
Some of the leaves it starts in the middle, and some are splotched looking almost like light bleaching.
Any thoughts would be appreciated, thanx in advance.

Flood n drain
PH 5.73
water temp 65
PPM's 1200
feed 4x day
Air temp 72
RH 50

So much for that idea, guess I'll try some where else.

stem looks very red could be start of some deficiency. possibly phosphorous or mag. or it got cold in there possibly? some strains do this but it looks like the jagged parts of the leaves are turning yellow. just a guess i dont do hydro

not Mg. Looks more like K.

That wouldnt be enough for me to start messing with the nutrients esp if the other plants in the tray are looking fine. I would wait until it progresses before I did anything.

Thanx for the replies, it did get kind of cool in there for about a wk at night. They only have a cpl wks left and i was going to reduce nutes. Didn't want to take a chance on causing further problems.
Notice the leaf in middle of pic how it;s splotchy?