Disclaimer, I would not call myself an experienced grower by any means.
With that said, your plants do not seem to be praying overly much and due to how many lower growths are experiencing similar symptoms I do not believe it is light burn - although this could be part of the problem.
If I had to guess I would say it's a little to heavy on the feeding side (especially if your TDS meter uses the 500 scale). I know of people who push their plants to 1800 ppm (700 scale) and have great results but those are for BIG girls very late into flower (this is for daily feedings).
If I were you I would leave the light on its previous setting and dial back the nutrients and see if the problem persists. If you change the light and the nutrients at the same time you may have some trouble telling what caused the problems.
Otherwise, your plants look great man. A couple of yellow tips here and there aren't going to do anything in the long run.
Best of lucky buddy.