Yes, I was a little stumped by this "non- fish" renovation too. I reckon the missus has put a little seed in his head about a swimming pool, which of course he is cunningly playing along with, until......
in a few months time he's proudly displaying pictures of said pool, stuffed to the gunnels with fish, and his missus is sat on a deckchair at the side with a face like a bulldog chewing a wasp!!