yellowing of my leafs not sure if normal death process

so i have about 20 days left in my flowering cycle and some of my plants leafs are showing this, is this the normal yellowing process of the plants leafs or something else?

that looks like some wicked awful nute burn...how does the rest of the plant look? What is your pH? is this new? How long has this been going on if it wasn't like sudden?

The normal dying you look for is like a gradual yellowing of the lower leaves moving up the plant as you get closer to harvest...that looks neither gradual or healthy...when plants are in flower taking nutes from leaves to make buds the leaves will start going pale and then paler and then totally yellow and kinda limp...like a really really really lsow sucking of something up through a straw...it is neither sudden or drastic, and there is only browning if you let the leaf stay past the yellow limp obviously dead stage...it will eventually dry up and just fall off, but that right there is no good...

well its pretty much just the two leafs on my one plant some other leafs are kind of showing the same signs i haven't been giving any nutrients to the plants at all during the flowering stage the water i have been using to water is coming right from my sink i haven't treated it to change the ph could that be the problem?

so could this be caused by an unbalanced ph level?