A "rich" soil will not cure all problems although a soil that is well balanced will. Far too many people amend their soil and add heavy doses of fertilizers, often the wrong ones, which really compound the problem. A well balanced soil, one with ample levels of organic matter and a pH in the 6.2 to 6.8 range should have ample nutrients available for tthe plants growing there when the plants need them, just not a large quantity of "stuff" now and very little later because water has moved those nutrients out of the soil and into the ground water where those nutrients are pollutants. A large part of Integrated Pest Management is knowing why some problem may exist (poor soil nutrition often) and fixing that root cause.

I see episodes of tomato septoria often in summer, but don't see how disinfecting cages might help. No research has ever shown active contamination by equipment, and I've never noticed an association. Straw mulch has been found to suppress septoria, but since there is no resistance available, you d what you can. I cluster tomatoes in several spots in the garden -- 4 plants here and 6 there -- as a preventive measure. It's been my experience that when cool rain sets the stage, septoria will sweep through one bed but not another. The edges of the woods are full of horsenettle, and I think that's where the inoculum comes from.

The treatment of choice for most people is spraying with fungicides, usually copper based, but you won't get much backing for that idea in this forum. I don't know about septoria, but I understand that late blight needs host plant material all the time to survive (which is why crop rotation can work) and soil fungi are supposed to clobber late blight, so that seems to point to housekeeping and/or sanitation problems over the off season. I had this problem back when I lived in Exeter, but not here in Tucson, so I'm weather-lucky. In New Hampshire (damp and cool) we kept plants well separated and viciously nipped back. It seemed to work well.

Re: the nutrient issue-- there are folks who post here who grow hydro who may see your post, but I would also ask the hydroponics forum in the meantime. The pale leaves with still-green veins looks like an early nitrogen and/or mag deficiency, but hydroponics is a whole different deal than growing in soil, As for the lesions... It doesn't look like spray damage to me, and it doesn't look much like Septoria. It might be the start of the concentric/target pattern in other diseases like EB or target spot, and botrytis is also a possibility, especially considering the paleness of the lesions. I did spray with a fungacide to kill aphids. Is it possible the fungacide spray caused this? Aphids are not fungus. I guess some fungicides may be somewhat toxic to aphids, and the simple physical action of liquid being sprayed and running off is good at knocking back aphids because it washes them off. A lot of people use just plain water and squirt off the aphids with a vigorous spray. That approach tends to work best outdoors, though, where there are beneficial predators to clean up many of the straggler aphids. If you continue to have aphid problems, you'll need to get something like insecticidal soap to more directly and efficiently address the aphids. Fungicide is an inefficient way to kill insects if it is effective at all. EDIT: if you're using neem, it can work on aphids AND fungus. That said, you apparently needed a fungicide anyway, so it worked out for the best. Are the spots limited to just the leaves in the photo or has it spread to other places on the plant? If only on the leaves in the photo or just a few leaves here and there, I would document well with photos in case you need to refer to them later, prune off the affected foliage, and repeat fungicide application in a week or so. What fungicide are you using?