The way I tell if my ppm's are to low or high are of course how the plants look but also I set my top off to same ppm as my system and if my ppm are 50+ lower than day before, they need to be raised, if there the same or higher they need to be lowered. Everyone and strain has different ways and likings to where its at and to how much thier eating but I like mine eating anywhere from 10-30 a day, usually 20, then I just bring em back up daily. 460 seems pretty low but your girls are looking great and seem to be loving it and if you raised em before and they showed sighns of burning they must be good where their at, but keeping track of what there eating I think is the best way to keep track of what they need. Keep it up, those strains look like there some wicked smoke, I want some Quarkle and LA Conf., sorry know you said already but is this your first grow with these strains, if not which yeilds higher, I heard Quarkle yeilds low but is straight murder, but idk at all other than what I read that one time,how do you like the yeilds.