this happened after flushing,right? since there wasn't serious nute burn signs on the plant in previous week's photos,you have managed to let the plant absorb all nutes left in the medium with that flush.then it wanted some more.This is why leaves turned to yellow,plant started to drink from its leaf reserves.those rusts are because the plant lacked P and K after flushing.not a big deal.250ppm runoff water is something really good.you are going to have a smooth smoke. I'm not flushing plants that dont have nutrient burn signs,I don't want to starve them and lose their leaves.Even if I flush,I add a normal feeding solution right after flushing.