Hey Craiggiles welcome to the PBF!!!
Although DG8 is correct with his answer I am sure Sue could help you out for sure. I will give you my non professional answer and you can take it for what it's worth.
By looking at your pond if it were me now... I would setup 3 stations with 2 fusers on each station. Imagine your pond being at the bottom of a clock if you will.
I would put a station at 8, 6 and 4 o'clock. Or I would put 2 stations with 3 diffusers at the 8 and 4 o'clock spots.
With either of these setups I believe your middle of your pond would get mixed pretty good.
Remember though I am no expert/ installer of air. I'm just a read a lot do it yourself kind of guy!
Good Luck and keep us posted,
RC