Yellow leaf problem

hey guys,
My white widow plant grows in a custom made box, I use 250w HPS lamb for flowering, the problem is leafs at the buttom part of the plant gets yellow or rotten, I usually remove them from the plant but not sure if that is the solution for that?
Only the leafs at the buttom part of the plant gets yellow rest is very healthy, I think its because the light which doesnt reach the downer part of the plant.
what do u say?

are nutes splashing on these leaves when you water?

Marijuana Plant Problems and Cures

Leaves turning yellow at the lower nodes are typical in flowering. The more advanced the bud development, the more fan leaves that will drop. Without pictures, its hard to be certain. As a rule of thumb, if fan leaves are turning yellow in a somewhat uniform fashion (versus spots, or burns) this is usually normal. Typically you will see the larger fan leave drop first then the the more moderate size following afterward.