I donā??t know what stage of grow Ur at but I'll tell you what I have experienced. There have been only two times I have ever seen yellowing of leaves 1st lack of nitrogen, which I have come across in my last two grows which I have put that down using different nut's this time and 2nd the plant is coming to its end of its life. The second is where I see the most of what you describe when u say a couple of them are actually yellowing slightly yet showing signs of over fert at the same time but this usually happens around 8th week of flowering but I have also had it happen to me when I had to flush some plants at least thatā??s what happened to me. Or maybe it could just be that these plants have bad genetics, just didnā??t root well or wasnā??t a good clone at time of cutting also it can take a while for the plant to sort its self out depending on how bad she is. I donā??t claim to be an expert man but when things go wrong and they always do for me with nearly every grow I go back to the start and stop everything, just feed water and watch them like a hawk, If things get better you know u overfeed them if they get worse then it could be the water or soil if things stay the same then thereā??s something missing like I said yellowing can = a nitrogen problem, but thatā??s what makes growing interesting although ur probably cursing all that crap right now I have purple/red stems on most plants I grow and donā??t know why but thereā??s never been anything wrong with the bud but like I said no expert just thought I'd chirp up seeing as no one else wishes to say anything plus nothing else to do OJ man, hope u get Ur problem sorted