What were the symptoms of the plants that died in your prior grows? When did the symptoms appear, and how long did it take for them to die? I am a bit concerned that your soil composition and watering style may have contributed. The clay may be impeding water movement and locking up necessary ions. You mixture is fairly nutrient and salt dense, and since you aren't watering through and you've got clay in the mix, my concern would be root suffocation and salt build-up. But other than looking over-watered, your plants look fine.