First Grow. Help! Brown Leaves

This is my first grow and I'm having some issues with my aeroponics system. My plant is flourishing and doing great except the very lower leaves. They turned brown on the tips and is working it's way toward the middle, they never turned yellow and then brown, they started off turning brown. The bucket solution was switched about 3-4 days ago and they were brown before I switched it. Also the brown leaves are not stiff or hard, they are soft like the healthy ones. Check out the pics and let me know what you think.

I dont know shit about aeroponics but looks like nute burn to me.

I wasn't sure if it was nute burn or not, I thought it was nute burn when the leaves turned yellow and then brown. Mine never turned yellow. Can nute burn cause both 2 happen? The brown and yellow.