Leaves disappearing from tomato plants

[Eric K]

I purchased a small hydroponic system and am trying to use it to grow tomatoes. I inserted the tomato seeds in the sponges, filled it with water, and added about a half a teaspoon of solid tomato nutrient.

The plants grew well for a few weeks, then began to droop. I figured they needed more nutrient, so I added another half a teaspoon of nutrient to the water. The next day, the leaves all disappeared. They didn't fall off, they disappeared. Now there are just stems with no leaves.

I am very new to this. What would cause this to happen?

EDIT: The stems are now disappearing, and there are bite marks, so I am assuming it is cockroaches or other animals. I will have to spray the leaves next time.