back lights off to 4inches.take another cup same size and soil mix as the one ur growin,weigh its dry weight,wen cup ur growin in weighs that amont water.wen plants get bigger u mght find urself watering a ounce sooner then the dry wet,on a scale.no ferts at this stage.i dont know how much water ur given,but mine at that stage under those type lights,average 1-1and 1/2 ounces,i use tap water 7.4 andprefert. soil.