Brown spots on leaves (not deficiency)

So i have in my past had issued in dwc with plant leaves starting to get brown spots and it spreading, pretty much until the entire effected leaved dry and die off. I spent at least a month pretty regularly researching causes and testing various methods to correct what i thought was some kind of deficiency/toxicity. As much research and "troubleshooting" as i did, i could not find nor eliminate this vicious epidemic..in my time spent researching i also found countless other growers who had this same exact dilema with it ultimately going undiagnosed..it wasnt a deficiencu or toxicity nor was it a ph meter error or fluctiation issue..
Come to find out that my issue was my humidifier..the filters that go on mine dont last very long without needing to be changed amd build up this brown fungus type residue..that plus my using tap water ultimately resulted in these brown spots that grew and engulfed my plants leaves..
I cant say this is the reason that all other unexplained cases had the same problem, but i found it to be the issue in my grow.
Most of the more experienced growers probably knew this, but i was on my 3rd dwc grow, so for those who encounter this issue, make sure to use RO water in your humidifiers and do regularly check those filters!!!

Fantastic post OP.
Very informative.
Experience speaks a lot louder than words.

Thanks man. This was an issue that even some of the most experienced people were stumped on..it can be the most simple of things that we forget to check on in our grows..hopefully this helps someone in need