no you can for faster grow..normal is 18/6 but ive seen grows with as little as 12/12...they will flower early with less light though so id recommend more
if its possible to get more light for them there growth will be considerably larger
sugar yeast and 2 liter bottle is a cheap way to do it..lasts about a week before u need to add more
if u have the money co2 generators are also available