6 weeks into flower; getting yellowing leaves.

That's what's really weird! The Jack Herer was WAY higher (6.8 in 6.2 out and 1600PPM) while the Northern Lights was 6.7 out and 455 PPM! (I tend to feed them the same thing at the same time; the NL is much larger) The PPM readings are suspect because a couple of times the ppm went UP even though no nutes were added since previous watering! (Is this a sign of nute lock?) Assuming it might be, I did a full flush. After flushing the runoff were Jack H: 6.7/511ppm and N. Lights: 6.2/773 ppm. Not sure if it's advised or not, but I did trim and remove most of the yellowing and discolored leaves today. Also, they look like getting close to harvest. Still a lot of aphids (WAY less than before) so plan on doing a "wash" after harvesting. Any suggestions/comments?

@John Curry As organic nutrients break down, they increase the PPM. So that may be why you're seeing an increase in PPM without feeding. Hopefully the flush helps ya. Being close to harvest like you say, I wouldn't panic too much about the yellowing. More info on battling aphids: https://www.mrgrowit.com/post/aphids-on-cannabis-plants