A good thing to do is to remove any obviously dying leaves, cut them off right where the dying leaf's stem is at the main stalk. Also remove dead leaves if they fall on the soil ot anywhere else in your grow. Yellowing, dying leaves are beacons to bugs of a great place to start attacking the plant. Captain Obvious here, what's the PH of the soil? Hang tough bro, they ain't dead yet. Considering the first photo (last try you said), the middle photo plant is an improvement.