Zinc def or something else?

This has been happening for the past five weeks.just seems like it spreads from plant to plant.they eventually get so bad i throw them out and start over.the strain is good because my friends plants look great.someone said it looks like a zinc def and another said a virus.i have tried flushing them with ph water(6. and refertilizing them(1/2 strenghth).nothing seems to work.
It started happening when the weather outside got cold.my grow room temp has stayed the same(78 degrees)could the cold weather have affected my tap water causing a zinc def or is it something else?
Any input would be appreciated

root rot. my first grow ever had the same shit. turns brown next and then mildews up

thanks for the reply.you really think root rot.i dont overwater.those particular plants have only been watered about 3 times in 20 days

dont give your plants freezing cold water, that could be it, uptake gets blown when u use icy water. i listened to some assholes here and there on the internet that said giving your plants cold water makes "cool colors maaan"

give them lukewarm water the roots grow better in it

weed is all about roots

of course,i always water with room temp water.i wish that was my problem.