Thanks everso much you lot! The light (250 HPS) was only 18" from the top of the seedling (about 10cm high). I think I got my wiresa crossed on something I read previous. I have no fan in there at present. The only ventilation is 2 vents top and bottom of the cupboard. My space is around 3ft by 3ft. The water flow has been ok though, I did wonder if I had to have the micro pump vent fully open with full jets coming out of the drip ring...but I rang the company i bought it from and they said it only has to drip. It must be the light, and ventilation. Do I have to prepare my hydroton pebbles first? I was told to clean them first to get rid of any sediment, then to soak them in nutrient solution before starting. Is this correct? Also, is it good practise to hand feed the seeedling sometimes during the first couple of weeks to get it started, and to get a root system on the go?
MASSIVE thanks to those who replied. beleive me I NEED the guidance.