"David Hare-Scott" writes:
How about diesel oil?

That's a thought, but I have reservations. The strong smell of fuel
would probably have the neighbours calling the fire brigade. The
pool's surface area is so large there is a lot of evaporation. When
I put kero on a 0.5 sq m pit drain outside our back door there is a
strong smell of kero inside for 48 hrs as the lighter fractions
evaporate.

Use a natural method - chuck in a few fish.

Not a very promising idea in a building site. Cement or mortar will make
the water too alkaline for fish and there has to be some sort of ecology
to support them.

I ruled out fish in my original post. Discounting the kookaburras,
I'd have PETA on my back each time the sun comes out leaving half
the fish thrashing about in mud for a day or two until the next bout
of rain. There is the pool itself, and the water-filled craters in the
surrounding yard, both breeding 'skeeters.
--
John Savage (my news address is not valid for email)