brown patches

Hey guys, Just wanted to make a post asking for help with some brown patches I’ve been noticing on one of my plants. They developed a little less than a week ago and have quickly spread to a number of other leaves on my plant. I’ve been trying to diagnose the issue, but I’m unable to find...

So my plants got a bit older, I had this issue on the very first leaves and they seem to be moving up to newer ones. I've scoured all the image charts and tried to find a cause to the problem, can't really find any causes that match the symptoms. I've added cal/mag in case its a calcium...