Leaf tips browning and leaf drop. Disease?

[Chile Jim]

I suspect my pepper plants, but also tomatoes and eggplants have some form of disease/pathogen. They start healthy and then at various growth stages, the leaves turn brown at the tips and then the leaves drop. The plants never recover.
 
Pretty sure it's not under/over watering or over/under fertilizing as they turn from very healthy to sickly pretty quickly and at various growth stages.
 
Has anyone seen anything like this before? What can I do? HELP!

 

 

[Mr. West]

idk about diseases, but the deterioration of leaf tips and margins is symptomatic of potassium deficiency and salt toxicity.
What's your potting mix and ferts?