if no cracks are visible, the leak should be in a line entering or exiting the pool ...
1. get some red or grape food dye in a squirt bottle & swim goggles,
2. fill the pool to create more pressure
3. squirt some at the inlet & outlets ...
... you will see which inlet or outlet sucks your dye .... dig the line up & cut out & replace the broken/cracked line
best wishes