Thanks for your responses everyone, its my first time posting here.

But I'm getting some mixed opinions which is to be expected with such a variable, wild and wonderful plant!

So, Stinky, you don't think it looks like overdoing it of the nutes then?
I was considering a flush with plain water for a few days but they are so green and lush that it didn't feel right to do it.
If its not nute burn then could it be nute defficiency?
My RH% is between 40 and 50 and the temps are between (60 and 70 night/day).
The PH is always between 5 and 5.5 but is it possible this is too acidic?

Its only a 400W metal halide and it didn't feel too hot on the back of my hand so I thought they were safe. And it is also present on plants that aren't as tall as that one and are not directly under the light like he/she is which was another thing that pointed away from that for me.

But Klondike, I have had these lights in the past and 6 inches is definately far too close as that would burn my hand after a few mins!

Thanks again everyone and if you have any more thoughts they will be most welcome.