Please help! center of leaves turning brown! PICS!

I just checked on my plants when my light turned on and i noticed that one of them was not looking so great. my ph is under 6, my ppm is around 270 with no nutrients, just r.o water and calmag. it might be hard to tell in the pics but the center of some of the leaves are turning brown and the tips of the leaves are starting to curl up. Please let me know what you think it is! thank you!!

Im a newb also and grow in soil , but you might want to look into fungus or mildew on your roots.

my roots are just starting to pop out of the pots and they look really white and healthy and strong. my res temps don't go above 72

Smell the roots

If it smells then yeah look into the cure to root rot aka how to breed beneficials, it will be the quickest and best way out. pretty easy too don't be scared of the ingredients you'll need

A last resort is h202 bath and less waterings/more frequent waterings(dep. on situation) then running small amounts of bleach or h202 in the reservoir, and cloning it when it finally gets some healthy growth to save the genetics

sometimes roots initially die because they were underwatered, then watering frequency is increased and that dead root is what spreads to the rest of the plant, in a sterile environments you'd be checking the roots out daily so it won't happen but with organics (which you should do now) it will eat that dead root and stop the water from becoming bad so quickly.

sometimes its only because you are overwatering the plant,

well the roots haven't fully poped out of the net pot yet but some are starting to show out of the sides (see pic). i can't really smell them now but i did some rearranging with my grow room. i think that my a/c intake was blowing straight on the plant, and at night it became a little much. i also lowered my light about 2 feet. i thought i was wasting a lot of light