When I run soil I tend to start somewhere in the 6 -6.2 range and increase as they grow, late in flower I'm up 6.6 to 6.7. As long as things look healthy, I'll vary that a little, kinda up down up, making different things available. But... there is a rise from seed to flower. And yes, it could be excess phosphorus f'ing with your calcium... unfortunately symptoms are the same... this is for the "on site tech" to evaluate!
That'd be you!