When plants enter the final stage of there lives often some leaves yellow, grow looks good, keep an eye on them i really dont think this is much of an issue but if it continues you may have a small deficiency, next watering check ph it may be a bit off. All i grow is autos and this happens more with autos at the end, it may continue as it looks like your pretty close to the end, a tip when running autos do not run multiple strains as different autos, autos grow at different rates and some are hardyer than others, the tallest plant will force you to raise your light and smaller strains will suffer, allso different strains of autos react differently to feeding what is fine with one strain may make another unhappy as you know autos need much less food and nutrients than there photoperid cousins what may be fine for 1 strain may negatively affect another, as you know you chop by your trichome if you still have pistols that have not turned give plants cold water this will flip the trick. Just nextime you water check ph that will give you a clue to what is happening you may have to reduce the amount of flower agent for that strain.
