plants wilt and the roots turn brown
 

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.

The mix for the calcium nitrate is 1/3 to 3/4 tsp as the plants mature. I don't know if that would help. The mix also could be to strong for a low nutrient user like lettuce.