With a high degree of certainty juddjonas we have a minor issue with Magnesium uptake effecting the lower leaves. I say we because just an hour ago I found three of my own plants with the same issue.

It doesn't mean we need to add magnesium at this point because competition of other excessive fertilizers will suppress magnesium uptake. Excess potassium, ammonium or calcium fertilization will do it and I see in your pictures you have nice dark green leaves, suggesting you don't skimp on the amounts of fertilizers you use. If you haven't added any Magnesium ever you can, the choice is yours and you can use magnesium sulfate. (Epsom salt).

Three days ago I added potassium nitrate, calcium nitrate and potassium sulfate and may of over did a few plants with the potassium so I'll wait it out because I know when and how much magnesium I put in my soil from day 1.

It's not the end of your plant. Magnesium is mobile in the plant meaning it will move from the older and lower leaves to the newer leaves and what you are seeing now. If your plant has a heavy yield of tomatoes hanging on your plants now, like I do, the excessive fertilizer will be pulled up by the plant and used quickly with normal magnesium uptake resuming shortly after. Those leaves may die but losing them won't hurt the plant a bit and if you decide to add Epsom salt a teaspoon or two per plant will work. Epsom salt is 9% magnesium I believe so you're not adding much.

A pic of one of my leaves taken not long ago and another of my amazing tomato plants just for kicks. The first two rows are determine and the back row and first ones on the right are indeterminate plants.

Wow, you have quite the operation going! I like seeing other peoples gardens. I'm fairly new to gardening, only been at a few years (but with some success!). I'm in an urban area and can only grow exclusively in containers and grow bags. So if it's a magnesium issue, would I just dissolve epsom salt and water it in? This kind of ties into another question that I have here about fertilizing during a long stretch of high heat. Maybe you can weigh in on that if you have time. Thank you so much for the response. Every season I learn so much.

Honestly I've never heard or read anything about fertilizing during high temperatures but I do no matter the temperature andbased on a time table using the plants growing stages to determine when, what and how much. I read everything I can find on the subject and not the how to by a blogger but university studies, commercial grower guides from every agency in the US including overseas, the list goes on and on. I have a excessive obsession on the subject.