Veggies, Disease, and Mineral Deficiencies?

Well, it seemed about time for an update, so I thought I'd post some pics of the veggies. For the most part, things seem to be going very well. The squash has been productive and delicious, though the leaves are yellowing, get these splotches on them, and eventually wither and die.
I thought there was a serious mineral deficiency going on with this cucumber, but it turns out that it's some sort of white cucumber hybrid. Park Seed calls it "Cucumber Pearl", and they threw the seeds in with my last order. They taste good.

The peppers seem to be going OK. They were struggling for a while while their roots got long enough to stay in the water, but they seem to be doing well now.
The tomatoes are doing great! There are several large tomatoes on the vine, just waiting to turn red.
So, not knowing anything about minerals, mineral deficiencies, pests, or basically anything about hydroponic gardening, I thought I'd throw these photos out there in case someone who did know something about anything could respond! I've been adding 5ml iron and 30 ml of Potassium weekly, with an occassional blast of Kalkwasser to supplement calcium and help keep the pH up. I guess it's not enough for the squash, but seems to be OK for the other stuff. Again, I don't know.