Thanks all.

It is just white marble plaster.

By my calculations, it's filling at 650 gph and should be done around 8am.

BTW, here's a good tip I got from my pb - it's probably been posted here already but it was new to me... When filling your pool, if you are nervous of overfilling during the night, DO NOT turn the water off. Reduce to one hose and cut back the flow to just a small amount if you think it is necessary. If you turn the water off before the pool is full, you may end up with a ring at the water line - like a ring in the bathtub.

I'll try to get a picture up tomorrow once it's full.