Tomato plant ailing
I have read and read and read, but can't find anything that seems similar enough to my tomato issues. I am using a tomato container kit that has worked well for me in the past but this summer, my tomatoes are showing yellowing leaves, some brownish as if lacking water, although new growth is nice and green and healthy. I have fertilized it; it's a self-watering container so I have kept the bottom resevoir full.
Perhaps I am just not experienced enough to see it is the same as other photos of diseases, but it just doesn't quite seem to fit ones I have read.
The photo shows the yellow leaves on old growth. The new growth is hearty and green.
Thank you in advance for any insights.