Possible lack of food

potting soil was used ,they are 6 weeks old ,all of the plants are doing this light green some yellow bad and dieing ,two strains going same happening to both ,nothing has been fed to them ,ph unknown, ec unknown , conditions Temp 23 , humidity has been keep low ,possibly need to put light up a few more inches , 6oo hps dual spec ,all plants were healthy and just slightly loosing greenness about 8 days ago

You need to feed them. Do you have nutrients already?

Whatever you feed don’t do it full strength.

Listen to @hotrodharley ...begin feeding at 1/4 recommended dose, see how they react...if favorable next FEEDING time, up it slightly.
FF

This is lack of food aint it ,what can I get diy style fir them today like from tesco of from my cupboard, cheers guys info would be very well received

yes, there lacking in nitrogen by the looks of it