burn fan/sugar leaves

Not sure re what's going on but this just happened today when I checked them this evening.
Yellowing leaves lower down( some falling off)
They are about week 5-6 of flowering
They are about 18" away from a 1000 watt light
Humidity around 45-50
Temp when lights are on is about 27 and about 20 I. The evening mabee a bit lower
Tap water usually is around 7 ph
I'm growing in pro mix with extra perlite, mabee not enough if these are root bound( not sure if it's what happening)
They are fed general hydroponics flower formula for soil, 5mls per 2.5 litre feeding. I haven't fed them in awhile though, about a week. I flushed them all with 5 litres of water each and now it seems to have sped up whatever is going on!
Frustrated and lacking the knowledge needed, can anyone help?

I think it looks like light burn. You'd be better off having that 1000w up a bit high 24 inches or so. Maybe water or reflection caused it to burn right there or maybe just to close to light. Sometime bud rot inside the bud causes fan leaf to die and it kind of looks like light burn too so check for mold on that bud too.

Those would be my guesses anyway.

Yea how about some fAn action aimed right at that atmospheric area from top of canopy to the light... i get you can still get light burn but its prob a bit warm there too....

I've lifted the light up to see if that helps but I don't think it's the issue.... time will tell
I turned on the lights to look and saw a few others doing in and now the leaves on top are suffering more

Those look like hot spots from you light being to close. How many ppm are u giving them when you do feed them>? If you are just giving them water most of the time the leaves are going to start going yellow. What gh nutes are you giving them, floranova?

I don't measure ppm as I have gotten my hydro setup yet, just measure and water

I thought it might have been because I flushed them yesterday

I've moved the light up about two feet above canopy mabee a bit higher to see if that helpe