thanks for the responses.. i'm shying away from nutrient burn - nothing has been used except good compost... i've over-ferted before and i think that usually its the tips of the leaves that suffer the most.. I checked the smallest of the plants tonight, a couple of the leaves had turned up and basically dried out so I'm thinking lights too close.

I figure that its all sheeted with mylar floor to ceiling, there is ventilation but probably not enough, so i think they've literally cooked a little - well at least i know for the future!

Thanks for the comments.. will post with an update soon - even with these slight problems, i've never seen plants grow so quickly!

mjd