plants wilt and the roots turn brown

[Roy]

I am having a problem with my nutrient solution. I use miracle grow, 1 tsp per gal. This works fine. The problem is when I add the epsom salts and calcium nitrate at 1/4 tsp per gal, the plants wilt and the roots turn brown. I have a 12 gal tank and about 60 lettuce and Brocolli plants in an nft system.

help.