Low ppm runoff

Im about to harvest and im flushing. I checked the ppm and it was 600eu ppm that seems relatively low to me im not complaining about low salt levels but my understanding is that is should be higher after a 4 month feed and no flush yet(b4 now). These plants are large 3ft wide 4.5ft high. Questionis should i be upping my nutrients being that they are larger plants? Thank u. Indoor btw

without pictures it is very difficult to say something...sorry

when they are looking healthy then go straight on with what you are doing