Disease or deficiency?

[clkingtx]

Hello,

I have been having some yellowing leaves on my tomato plants. I am not sure what the problem is. I have been pulling them off as I find them, and many plants don't have any more yellowing leaves, but new plants are still getting some. Is it some sort of deficiency or something else. The closest picture I can find is of salt burn in leaves, but I don't know if that is what it is. Here are a few pictures...