for the moment i have turned off one light and left only 1x 600watt hps on and raised it another 6 inches as i have no magnesium supliments yet but it is only the plants directly under the lights that are effected, all the outer plants seem perfect. they have stretched a little, about 3 - 4 inches but they are exteamly packed with nodes showing very little of the internodes so i guess they still have a lot of stretching left to do.

will purchase some new bulbs though tomorrow and see if it helps, its long overdue. will get some salts too and give that a try.
i do normally water about one third of the pot capacity and when feeding but by the next day the pots are dry and light in weight so i asume they need watering again.

thanks again the help is appreciated