My hydroponic tomato garden keeps dying.?

I set up a hydroponic garden in my basement. I tried out tomatoes first because I read hot 100 tomatoes are the easiest thing to grow. I have a 25 gal plastic tote with holes cut out of the lid where I dropped in my net pots with my tomato plants in pea gravel and my grow lights 4 inches from the top of the plants. I grew my plants in MG top soil for 4 weeks before washing the roots and transplanting them into the tub. I'm using MG 20-20-20 water soluble plant food. I followed the instructions 1 scoop per gal. The plants do great for a week then they start to wilt and die. The water in the tub becomes foamy and starts to bubble a blue foam to the lid of the tub. This is the 2nd time this has happened. Any suggestions?