Yup i can say for me at least for the girls I've grown 400ppm at this stage is well smack on,they really just want a ton of water right now but she will get potassium hungry also in spurts and keep blooming so you may notice those changes i was on about..
Its more of a case of when production becomes so little that it's counter productive to keep her around and not another girl in her place time wise. With some Dwc plants its been speculated whether they will even stop at all or just keep flowering. They wanna live forever like spartans
haha.