And powdery mildew. But they always get powdery mildew.
Solution to blossom end rot is to hand pollinate to ensure fruit set, wait till pollination takes, and then remove the blossoms by hand. You leave the blossoms on, and you increase the chances of end rot substantially. Not sure it being hydroponics or nah is relevant.
Additionally, these plants are monoecious, so you have to learn to ID the male and female flowers. The males are on long stem and have the anthers. Rip the petals off and it makes for a decent pollination wand.