I think I figured out what happened.

If you notice, in the front right of the grow box, I have a tube that runs down to the lava rock bed for bottom watering.

Well the other night when I watered with the super low pH, I watered right into the soil, bypassing the tube that surely hits the roots with the water flow.....but I use a 3 gallon jug to water and a lot of water prolly when right into the tube....

which is right next to the plant on the right.

It probably hit the roots with the super acidic water and nailed it hard....

The soil probably buffered it out which is why my flowering plants didnt get hurt nor did parts of my LST on the far left. The water never touched the roots bare like it did by the tube.

I keep a 5 gallon jug full of low Ph water and mix with fresh high alkaline and get a balance.

I ws stoned and used the super low pH water...

I'll post a pic of the gruesome aftermath tonight, they are sleeping right now.