yellowing/burnt lower leaves in early flower

Ive only been growing a few months and I havent had any problems with aphids knock on wood, but I have went a couple rounds with fungus gnats most likely due to my heavy handed inexperienced watering which I have been working on lol, but this picture( random pic from outside source) is supposedly damage caused by root aphids, I noticed it does strike a resemblance to your pic #2...what do you think?

looks pretty dead on, that's exactly the type of damage - showed the guy at the hydro shop some vid of the bugs I have and he said they're for sure not aphids as they move too fast and don't really look like them. they didn't have the stuff I wanted to kill them with anyway (botaniguard) so bought some pyrethrum stuff I'll use as a preventative in the other grow - he said it's probably due to using distilled water and that I shouldn't do that anymore. anyway, gonna try recovering them without doing an aphid cleanse first then fuck 'em I'll either toss them or try bayer advanced xD

I'll let you know what happens - any other input would be awesome too