Whats wrong here?

Hiya,
HSO Sour Diesel auto, DWC at about 4 weeks, 420ppm (Canna flores A+B) pH6.2. Leaves looking terrible. It was first on the big pair of leaves, i hoped it would stay there but its spreading.
My only thought is that i was away for a week and a mate checked the pH for me, i think it was in the 5.6 - 6 range and i thought maybe this strain needs a higher pH...?
Help!!
Thanks

Bump and cry for help!!
Rapid deterioration! I hadnt put a thermo/hydro in there when i did, 80%RH and 20°...i think that might be the problem...temps way too low, RH way too high.
Could that be causing these fucked up leaves?
To me, it doesnt look like nute burn (at 420 ppm not likely) or nute deficiency (cant see a 4 week old girl needing more than 420)
If i cant fix this she'll be dead in a week
Cheers!