The 1022 must have been replaced with another model (maybe the 1023). I would need to see a 1022 pump curve to make a good recommendation, but IF it performs like the 1023, I think it would run 6 diffusers nicely and as many as 8 so long as you keep the maximum depth of a diffuser less than 16 feet.

You should take into consideration that your pond more closely resembles a long skinny ditch with some wide spots rather than a round hole in the ground. For illustrative purposes, If you had a long skinny pond, like a strip mine, and you put a diffuser in one end...that diffuser will have little to no affect on the opposite end's turnover. Make sure you look at the far ends of your pond as separate "turnover" areas. For example...a diffuser in the big red square will not noticeably help the turnover in the yellow area.

The shape of your pond begs for at least 6 diffusers. IF the 1022 is similar to the 1023, then the pump wants to run 8 diffusers with the deepest on at 14 feet or so. This assumes 5/8" line runs as short as possible with as few fittings as possible.

Having excess turnover is a good thing, especially in your hot summer climate. If your system can turn the pond over twice a day, then you can run the system half as much which allows you to only run at night. This helps keep the water temperatures lower during the summer.

Try to get a pump curve for the 1022 and we'll go from there.

Fish on!,
Noel