Anyone know what's going on with this leaf?

Iv tried looking at a deficiency chart but not quite sure so thought I'd be best posting a photo. I only have two leaves like this out of the full plant, I was just curious what it is? The rest of the plant is fully green with no deficancys i can see.
I'm two weeks from switching to flower btw.

Its Calcium deficiency,but could be too much of something else.or ph to low.

Thankyou, I'll go and check my PH now