Brown Spots - Need advice please ?

These girls are in the first week of flowering @ 12/12 light.
the medium is Coco Canna and nutrition solution is Canadian Express.
I can say in terms of room, air supply and ventilation everything is fine.
lights are standing at 10" distance from them. after feeding them less than 48Hrs ago
these spots have appeared on 4 of them covering fan leaves.

Just to mention I have spray them with Water and Nitrogen ( 1ml per Litre)
is these spots are sign of Over Fertilising ? or some other problem ?

I appreciate any help, guidance and suggestion.

Many thanks in advance .

Peace

looks to be a ph issue need more info like ph ppm

Checking ph is what I always do first..it has to be at least close. It could be ph or possibly a calcium deficiency. I would flush with ph'd water and start nutes at 1/2 strength. The ph may be locking your calcium out

Hi Guys thanks for the quick reply !
I have kept the ph range between 5.8 > 6.5 and the Nutrition level stand between E.C 2.0 2.2 or 945 ppm - 1450 ppm

thanks again for your help

Are you spraying during lights on? The water droplets act like magnifying glasses causing burns.
Another possibility is spider mites. Look for tiny dots on the underside of the leaves.