Sorry to my prospective helper but it couldn't wait. Client bought a new house and the pool had been left for ages and was green and full of frogs. The plan was just to drain and clean it but once drained it became clear that wouldn't be possible. 70% of the floor was just held down by the water!
An hour and a half and I'm at this stage..
Plan is just to mosaic the floor to get it usable and do the rest in the autumn. I know, I know, but the rest of the house is swallowing far more money than they had budgeted for.