Thanks Guys,
The fan direction is no where near the plants so don't think this is the cause...
When I say the fan is running over the canopy, it basically blows across my bulbs with the slightest of air flow onto the plants creating a small movement across the canopy, if I was running a high speed fan directly across the canopy then I could understand but I really thinks it was the spider mite spray I used when lights were still on which had caused the issues.
I used the spray with 20 mins of light remaining as I saw spider mites , I turned the lights down to 600w and hoped it would be ok, but hind site is a fine thing
My lights on temp is 25 and the lights are approx 50cm from the tops so in my opinion it's the spider mite spray I used as opposed to any heat burn as they are just too far away to get burnt...
The leaves are crisping very quickly and I'm just hoping to reach 8 weeks to be honest.
I've put the feed back to where it should be at this stage so fingers crossed they will last the cause