Tony- I have a pond in Scottsbluff Nebraska that is similar in size to yours. I have trout in my pond and have had similar problems. I wouldn't run what they call a bottom diffuser Aerator in the summer as this will mix the water colume from the deep cooler water and mix with the warmer water on top, thus the trout will lose their cool water refuge on the bottom. I installed a Kasco top water splasher that i run only at night. During the night time this is when the o2 levels can drop as well as cloudy days. By using the top water splasher your not pulling up the cooler water. You say you have a irrigation ditch running in for your water supply, does this splash over some rocks or does it just run in the pond. If it just runs in the pond you probbly had a lack of o2 when the water heated up in the summer. I fill mine with ground water at 52 degress and let it run full time all of July and two weeks in august. This is the time of year when it is critical to keep temps down in our area as we don't have the cooler nights. In your area i cannot imagine (as i have spent time in the Springs) that you would ever have a water temp problem, only a oxygen problem. My trout (Scam) stress at 78 degrees and death is just arround the corner if i don't get it cooled down. If you would invest in a Top Water splasher you should be good to go. From what i know (Kasco) is one of the best and you can order one on the internet or find a place to purchase one. In fact there is a outfit in Ft. Collins that sells them i think. Check the yellow pages. I'm not an expert but the ole school of hard knocks taught me a lesson especially with the drought and heat of last summer. Once i put the Kasco in all problems went away. You can also run this in the winter to keep the pond open which you would want to do at those depths. Get a timer and run it at night and leave off during the day. I look forward to other posts to see if they agree with my comments. No drought this year up there is there!

jdm