Runoff low ph.

Hey everyone.
I'm using black gold organic soil and plain tap water. No nutrients
I've noticed for a while when I ph water or even nutrients to 6.5ph my runoff is well below 5.0ph. I have not used any nutrients since mid veg.
Now I'm having to ph my water to around 8.3 to get close to a 6.5ph runoff. What can I do to fix this problem. All fan leaves turn crispy and yellow.

Yellow fans it’s probably hungry. Without pics everyone is guessing.

I will add pictures shortly. Last time I gave nutrients instead of going yellow. It turn to a dry rusty leaf